Valorization of soybean pulp for sustainable α-ketoisocaproate production using engineered Bacillus subtilis whole-cell biocatalyst

The disposal of soybean pulp (okara) (∼14 M tons annually) represents a global concern. α-ketoisocaproate (KIC) is an intrinsic l-leucine metabolite boosting mammalian muscle growth and has great potential in animal husbandry. However, the use of pure l-leucine (5000 USD/kg) for KIC (22 USD/kg) bioproduction is cost-prohibitive in practice, while okara rich in l-leucine (10%) could serve as an economical alternative. Following the concept of a circular bioeconomy, we managed to develop a cost-efficient platform to valorize okara into KIC. In this study, proteolytic Bacillus subtilis strain 168 capable of utilizing okara as a comprehensive substrate was employed as the whole-cell biocatalyst for KIC bioproduction. First, we elucidated the function of genes involved in KIC downstream metabolism in strain 168, including those encoding 2-oxoisovalerate dehydrogenase (bkdAA), 2-oxoisovalerate decarboxylase (bkdAB), enoyl-CoA hydratase (fadB), and bifunctional enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase (fadN). Among those KIC downstream metabolizing mutants of strain 168, the 2-oxoisovalerate decarboxylase gene knockout strain (ΔbkdAB) was found to have a better accumulation of KIC. To further improve the KIC yield, a soluble l-amino acid deaminase (LAAD) from Proteus vulgaris was heterologously expressed in the ΔbkdAB strain and a ∼50% conversion of total l-leucine contained in okara was catalyzed into KIC, along with a ∼50% reduction of CO₂ emission compared to the wild-type cultures. Altogether, this renovated biocatalytic system provides an alternative platform to valorize okara for producing value-added chemicals in an eco-friendly manner.

SIRT3 controls brown fat thermogenesis by deacetylation regulation of pathways upstream of UCP1

OBJECTIVE

Brown adipose tissue (BAT) is important for thermoregulation in many mammals. Uncoupling protein 1 (UCP1) is the critical regulator of thermogenesis in BAT. Here we aimed to investigate the deacetylation control of BAT and to investigate a possible functional connection between UCP1 and sirtuin 3 (SIRT3), the master mitochondrial lysine deacetylase.

METHODS

We carried out physiological, molecular, and proteomic analyses of BAT from wild-type and Sirt3KO mice when BAT is activated. Mice were either cold exposed for 2 days or were injected with the β3-adrenergic agonist, CL316,243 (1 mg/kg; i.p.). Mutagenesis studies were conducted in a cellular model to assess the impact of acetylation lysine sites on UCP1 function. Cardiac punctures were collected for proteomic analysis of blood acylcarnitines. Isolated mitochondria were used for functional analysis of OXPHOS proteins.

RESULTS

Our findings showed that SIRT3 absence in mice resulted in impaired BAT lipid use, whole body thermoregulation, and respiration in BAT mitochondria, without affecting UCP1 expression. Acetylome profiling of BAT mitochondria revealed that SIRT3 regulates acetylation status of many BAT mitochondrial proteins including UCP1 and crucial upstream proteins. Mutagenesis work in cells suggested that UCP1 activity was independent of direct SIRT3-regulated lysine acetylation. However, SIRT3 impacted BAT mitochondrial proteins activities of acylcarnitine metabolism and specific electron transport chain complexes, CI and CII.

CONCLUSIONS

Our data highlight that SIRT3 likely controls BAT thermogenesis indirectly by targeting pathways upstream of UCP1.

Peroxisomal fatty acid beta-oxidation is not essential for virulence of Candida albicans

Phagocytic cells form the first line of defense against infections by the human fungal pathogen Candida albicans. Recent in vitro gene expression data suggest that upon phagocytosis by macrophages, C. albicans reprograms its metabolism to convert fatty acids into glucose by inducing the enzymes of the glyoxylate cycle and fatty acid beta-oxidation pathway. Here, we asked whether fatty acid beta-oxidation, a metabolic pathway localized to peroxisomes, is essential for fungal virulence by constructing two C. albicans double deletion strains: a pex5Delta/pex5Delta mutant, which is disturbed in the import of most peroxisomal enzymes, and a fox2Delta/fox2Delta mutant, which lacks the second enzyme of the beta-oxidation pathway. Both mutant strains had strongly reduced beta-oxidation activity and, accordingly, were unable to grow on media with fatty acids as a sole carbon source. Surprisingly, only the fox2Delta/fox2Delta mutant, and not the pex5Delta/pex5Delta mutant, displayed strong growth defects on nonfermentable carbon sources other than fatty acids (e.g., acetate, ethanol, or lactate) and showed attenuated virulence in a mouse model for systemic candidiasis. The degree of virulence attenuation of the fox2Delta/fox2Delta mutant was comparable to that of the icl1Delta/icl1Delta mutant, which lacks a functional glyoxylate cycle and also fails to grow on nonfermentable carbon sources. Together, our data suggest that peroxisomal fatty acid beta-oxidation is not essential for virulence of C. albicans, implying that the attenuated virulence of the fox2Delta/fox2Delta mutant is largely due to a dysfunctional glyoxylate cycle.

Peroxisomal localization in the developing mouse cerebellum: implications for neuronal abnormalities related to deficiencies in peroxisomes

In subjects with Zellweger syndrome, the most severe phenotype of peroxisomal biogenesis disorder, brain abnormalities include cortical dysplasia, neuronal heterotopia, and dysmyelination. To clarify the relationship between the lack of peroxisomes and neuronal abnormalities, we investigated peroxisomal localization in the mouse cerebellum, using double immunofluorescent staining for peroxisomal proteins. On immunostaining for peroxisomal matrix protein, while there are few peroxisomes in Purkinje cells, many locate in astroglia, especially soma of Bergmann glia. Clusters of peroxisomes were seen on the inferior side of the Purkinje cell layer in mice on postnatal days 3-5, and with time there was a shift to the superior side. The peroxisomal punctate pattern was seen to be radial and co-localized with Bergmann glial fibers. In cultured cells from the mouse cerebellum, peroxisomes were few in Purkinje cells, whereas many were evident in glial fibrillary acidic protein-positive cells. On the other hand, on immunostaining for peroxisomal membrane protein Pex14p, many particles were seen in Purkinje cells during all developmental stages, which means Purkinje cells possessed empty peroxisomal structures similar to findings of fibroblasts from the Zellweger patients. As peroxisomes in glial cells may control the development of neurons, the neuron-glial interaction and mechanisms of developing central nervous systems deserve ongoing attention.

Molecular epidemiology of sporadic breast cancer. The role of polymorphic genes involved in oestrogen biosynthesis and metabolism

The major known risk factors for female breast cancer are associated with prolonged exposure to increased levels of oestrogen. The predominant theory relates to effects of oestrogen on cell growth. Enhanced cell proliferation, induced either by endogenous or exogenous oestrogens, increases the number of cell divisions and thereby the possibility for mutation. However, current evidence also supports a role for oxidative metabolites, in particular catechol oestrogens, in the initiation of breast cancer. As observed in drug and chemical metabolism, there is considerable interindividual variability (polymorphism) in the conjugation pathways of both oestrogen and catechol oestrogens. These person-to-person differences, which are attributed to polymorphisms in the genes encoding for the respective enzymes, might define subpopulations of women with higher lifetime exposure to hormone-dependent growth promotion, or to cellular damage from particular oestrogens and/or oestrogen metabolites. Such variation could explain a portion of the cancer susceptibility associated with reproductive effects and hormone exposure. In this paper the potential role of polymorphic genes encoding for enzymes involved in oestrogen biosynthesis (CYP17, CYP19, and 17beta-HSD) and conversion of the oestrogen metabolites and their by-products (COMT, CYP1A1, CYP1B1, GSTM1, GSTM3, GSTP1, GSTT1 and MnSOD) in modulating individual susceptibility to breast cancer are reviewed. Although some of these low-penetrance genes appeared as good candidates for risk factors in the etiology of sporadic breast cancer, better designed and considerably larger studies than the majority of the studies conducted so far are evidently needed before any firm conclusions can be drawn.

Evidence for increased oxidative stress in peroxisomal D-bifunctional protein deficiency

Peroxisome biogenesis disorders (PBDs) and D-bifunctional protein (D-BP) deficiency are two types of inherited peroxisomal disorders. Patients with a PBD lack functional peroxisomes and patients with D-BP deficiency lack the enzyme, which is responsible for the second and third step of the peroxisomal beta-oxidation. The clinical presentation of these peroxisomal disorders is severe and includes several neurological abnormalities. The pathological mechanisms underlying these disorders are not understood and no therapies are available. Because peroxisomes have been associated with oxidative stress, as oxygen radicals are both produced and scavenged in peroxisomes, we have investigated whether oxidative stress is involved in the pathogenesis of PBDs and D-BP deficiency. We found in D-BP-deficient patients increased levels of thiobarbituric acid-reactive substances (TBARS) and 8-hydroxydeoxyguanosine (8-OHdG), which are markers for lipid peroxidation and oxidative DNA damage, respectively, whereas the levels of the lipophilic antioxidants alpha-tocopherol and coenzyme Q(10) were decreased. In addition, we found in skin fibroblasts from D-BP-deficient patients an imbalance between the activities of the peroxisomal H(2)O(2)-generating straight-chain acyl-CoA oxidase (SCOX) and the peroxisomal H(2)O(2)-degrading enzyme catalase. In conclusion, we have found clear evidence for the presence of increased oxidative stress in patients with D-BP deficiency, but not in patients with a PBD.

Dual activation of PPARalpha and PPARgamma by mono-(2-ethylhexyl) phthalate in rat ovarian granulosa cells

Peroxisome proliferator-activated receptors (PPARs) are key regulators of lipid metabolism and cell differentiation. The plasticizer di-(2-ethylhexyl) phthalate is a peroxisome proliferator, and its active metabolite mono-(2-ethylhexyl) phthalate (MEHP) activates PPARalpha and PPARgamma in cell transactivation assays. MEHP is a female reproductive toxicant and decreases activity, mRNA, and protein levels of aromatase, the rate-limiting enzyme that converts testosterone to estradiol in ovarian granulosa cells. To test the hypothesis that MEHP suppresses aromatase through PPAR pathways, granulosa cells were cultured with MEHP (50 microM) or selective activators of PPARgamma or PPARalpha for 48 h and gene expression was analyzed by real time RT-PCR. Both PPARalpha and PPARgamma activators significantly decreased aromatase mRNA and estradiol production like MEHP. The PPARgamma-selective antagonist GR 259662 partially blocked the suppression of aromatase by MEHP, suggesting that MEHP acts through PPARgamma, but not exclusively. MEHP and the PPARalpha-selective agonist GW 327647 induced expression of 17beta-hydroxysteroid dehydrogenase IV, a known PPARalpha-regulated gene, and induction was maintained with addition of the PPARgamma-selective antagonist. PPARalpha-selective activation also induced expression of aryl hydrocarbon receptor (AhR), CYP1B1, and epoxide hydrolase in the granulosa cell. These data support a model in which MEHP activates both PPARalpha and PPARgamma to suppress aromatase and alter other genes related to metabolism and differentiation in the granulosa cell.

Essential fatty acid synthesis and its regulation in mammals

The tissue content of highly unsaturated fatty acids (HUFA) such as arachidonic acid and docosahexaenoic acid is maintained in a narrow range by feedback regulation of synthesis. Delta-6 desaturase (D6D) catalyzes the first and rate-limiting step of the HUFA synthesis. Recent identification of a human case of D6D deficiency underscores the importance of this pathway. Sterol regulatory element binding protein-1c (SREBP-1c) is a key transcription factor that activates transcription of genes involved with fatty acid synthesis. We recently identified sterol regulatory element (SRE) that is required for activation of the human D6D gene by SREBP-1c. Moreover, the same SRE also mediates the suppression of the D6D gene by HUFA. The identification of SREBP-1c as a key regulator of D6D suggests that the major physiological function of SREBP-1c in liver may be the regulation of phospholipid synthesis rather than triglyceride synthesis. Peroxisome proliferators (PP) induce fatty acid oxidation enzymes and desaturases in rodent liver. However, the induction of desaturases by PP is slower than the induction of oxidation enzymes. This delayed induction may be a compensatory reaction to the increased demand of HUFA caused by increased HUFA oxidation and peroxisome proliferation in PP administration. Recent studies have demonstrated a critical role of peroxisomal beta-oxidation in DHA synthesis, and identified acyl CoA oxidase and D-bifunctional protein as the key enzymes.

Stiff-man syndrome: identification of 17 beta-hydroxysteroid dehydrogenase type 4 as a novel 80-kDa antineuronal antigen

Stiff-man syndrome (SMS) is a rare autoimmune disorder of the central nervous system associated with autoantibodies to glutamate decarboxylase (GAD). We isolated five brain-reactive human monoclonal antibodies, with reactivity distinct from GAD, from peripheral blood of a patient newly diagnosed with SMS. Two antibodies reacted with both Purkinje cells and ependymal cells, and precipitated an 80-kDa protein from rat neuronal primary cultures, which was also recognized by 12% (3/25) of SMS sera and 13% (2/15) of SMS cerebrospinal fluid (CSF) samples. The corresponding antigen was identified as 17 beta-hydroxysteroid dehydrogenase type 4 and may represent a possible novel target of autoimmunity in SMS.

Reinvestigation of peroxisomal 3-ketoacyl-CoA thiolase deficiency: identification of the true defect at the level of d-bifunctional protein

In this report, we reinvestigate the only patient ever reported with a deficiency of peroxisomal 3-ketoacyl-CoA thiolase (THIO). At the time when they were described, the abnormalities in this patient, which included accumulation of very-long-chain fatty acids and the bile-acid intermediate trihydroxycholestanoic acid, were believed to be the logical consequence of a deficiency of the peroxisomal beta-oxidation enzyme THIO. In light of the current knowledge of the peroxisomal beta-oxidation system, however, the reported biochemical aberrations can no longer be explained by a deficiency of this thiolase. In this study, we show that the true defect in this patient is at the level of d-bifunctional protein (DBP). Immunoblot analysis revealed the absence of DBP in postmortem brain of the patient, whereas THIO was normally present. In addition, we found that the patient had a homozygous deletion of part of exon 3 and intron 3 of the DBP gene, resulting in skipping of exon 3 at the cDNA level. Our findings imply that the group of single-peroxisomal beta-oxidation-enzyme deficiencies is limited to straight-chain acyl-CoA oxidase, DBP, and alpha-methylacyl-CoA racemase deficiency and that there is no longer evidence for the existence of THIO deficiency as a distinct clinical entity.

Molecular analysis of genomic DNA allows rapid, and accurate, prenatal diagnosis of peroxisomal D-bifunctional protein deficiency

Prenatal diagnosis was requested for a couple with a previous child affected by the peroxisomal disorder D-bifunctional protein deficiency. Prior analysis of the D-bifunctional protein cDNA sequence from the propositus had shown that it was missing 22 bp. This was subsequently attributed to a point mutation in the intron 5 donor site (IVS5 + 1G>C) of the D-bifunctional protein gene. Consistent with parental consanguinity, the patient was shown to be homozygous for this mutation, which is associated with loss of a Hph 1 restriction site in the genomic sequence. Prenatal testing of the fetus using genomic DNA isolated from uncultured amniocytes indicated that both alleles of the D-bifunctional protein had the IVS5 + 1G>C substitution. The peroxisomal defect was later confirmed biochemically using cultured amniocytes, which were found to have elevated levels of very long chain fatty acids (VLCFA). This is the first report of prenatal diagnosis of D-bifunctional protein deficiency using molecular analysis of genomic DNA.

[Diagnostic approach and treatment of inherited mitochondrial fatty acid oxidation disorders]

Inherited mitochondrial fatty acid oxidation disorders are a complex set of genetically-based diseases in which up to 22 different entities are currently recognized. Their incidence is probably underestimated because a high level of diagnostic suspicion is required for their detection. Their clinical spectrum and prognosis are variable. In recent years knowledge of these diseases and improved treatment have reduced associated mortality. A common characteristic of all these diseases is hypoketotic hypoglycemia, although this is not constant and does not appear in the short-chain disorders and, sometimes, does not even appear in the medium-chain disorders. Cardiac or skeletal myopathy combined and/or hepatic involvement at periods of metabolic decompensation are typical, since these tissues depend on fatty acid oxidation. Diagnosis has been simplified by the study of acylcarnitines in blood, even in periods of metabolic stability. Determination of acylglycines, organic acids, carnitines, free fatty acids and 3-hydroxy-fatty acids, together with enzymic and genetic studies, complete the diagnosis. In certain circumstances, a provocation test should be carried out. Treatment basically consists of avoiding fasting, restricting fatty acid uptake and increasing carbohydrate uptake, depending on the type of metabolic disorder. Pharmacological treatment may also be added (carnitine, riboflavine or carbamylglutamate).

D-bifunctional protein deficiency with fetal ascites, polyhydramnios, and contractures of hands and toes

Fetal abnormalities including chylous ascites, polyhydramnios, claw hands, and hammer toes were identified in an infant who had a missense mutation R106P and a 52bp deletion in the gene for a peroxisomal beta-oxidation enzyme, D-3-hydroxyacyl-CoA dehydratase/D-3-hydroxyacyl-CoA dehydrogenase, D-bifunctional protein. The patient had psychomotor retardation and craniofacial dysmorphism and died at 7 months of age. The patient had atypical fetal manifestations of this enzyme deficiency.

Peroxisomal straight-chain Acyl-CoA oxidase and D-bifunctional protein are essential for the retroconversion step in docosahexaenoic acid synthesis

Docosahexaenoic acid (DHA, C22:6n-3) is essential for normal brain and retinal development. The nature and subcellular location of the terminal steps in DHA biosynthesis have been controversial. Rather than direct Delta4-desaturation of C22:5n-3, it has been proposed that this intermediate is elongated to C24:5n-3, desaturated to C24:6n-3, and "retroconverted" to DHA via peroxisomal beta-oxidation. However, this hypothesis has recently been challenged. The goal of this study was to determine the mechanism and specific enzymes required for the retroconversion step in human skin fibroblasts. Cells from patients with deficiencies of either acyl-CoA oxidase or D-bifunctional protein, the first two enzymes of the peroxisomal straight-chain fatty acid beta-oxidation pathway, exhibited impaired (5-20% of control) conversion of either [1-14C]18:3n-3 or [1-14C]22:5n-3 to DHA as did cells from peroxisome biogenesis disorder patients comprising eight distinct genotypes. In contrast, normal DHA synthesis was observed in cells from patients with rhizomelic chondrodysplasia punctata, Refsum disease, X-linked adrenoleukodystrophy, and deficiency of mitochondrial medium- or very long-chain acyl-CoA dehydrogenase. Acyl-CoA oxidase-deficient cells accumulated 2-5 times more radiolabeled C24:6n-3 than did controls. Our data are consistent with the retroconversion hypothesis and demonstrate that peroxisomal beta-oxidation enzymes acyl-CoA oxidase and D-bifunctional protein are essential for this process in human skin fibroblasts.

Clinical consequences of defects in peroxisomal beta-oxidation

The disorders of peroxisomal beta-oxidation, which have been well characterised at the molecular level, include defects of acyl-CoA oxidase, defects of the D-bifunctional protein (D-BP) (including specific defects of its enoyl-CoA hydratase and D-3-hydroxyacyl-CoA dehydrogenase components), defects of the very-long-chain fatty acid (VLCFA)-CoA importer [X-linked adrenoleukodystrophy (ALD)] and alpha-methylacyl-CoA racemase deficiency. A survey of the clinical consequences of these defects indicates that defects in the acyl-CoA oxidase and D-BP can produce neonatal hypotonia, seizures in early infancy, retinopathy and progressive neurological dysfunction with leukodystrophy on imaging. Defects in the VLCFA-CoA importer and in the racemase do not produce disease until a long time after the neonatal period. However, again the clinical picture is dominated by neurological disease: impaired cognitive function with leukodystrophy in childhood X-linked ALD and retinopathy and neuropathy in racemase deficiency. It is difficult to escape the conclusion that defective peroxisomal beta-oxidation has effects (such as impaired neuronal migration in the developing brain), which are more serious than those produced by the accumulation of substrates (VLCFAs, pristanic acid) alone.

Molecular changes in the D-bifunctional protein cDNA sequence in Australasian patients belonging to the bifunctional protein complementation group

The cDNA sequence for the human D-bifunctional protein (D-BP: 17 beta-hydroxysteroid dehydrogenase IV) was investigated in patients with peroxisomal disorders belonging to the BP complementation group (CG). In three cases, analysis of polymerase chain reaction products generated from the patients' cDNA indicated the presence of a deletion within the region corresponding to nucleotides 209-537 of the normal cDNA sequence. Subsequent sequencing revealed that, in two of the patients, 47 base pairs were missing, with the deletion corresponding to nucleotides 302/3-349/50 of the normal sequence. In the third patient, a smaller deletion of 22 bp (nucleotides 280/1-302/3) was characterized. Only the mutant sequence was detected in each of these cases, consistent with parental consanguinity. Both deletions cause a frameshift, and would lead to premature termination of the BP. Available family members were also investigated, and the findings conformed with expectations for an autosomal recessive disorder. In addition to the deletions, a number of other base changes have been identified in this series of patients. In particular, one patient, whose parents were also consanguineous, was homozygous for a base change, which results in a nonconservative substitution of serine 177 with a phenylalanine residue. The functional significance of this amino acid substitution, as well as the other identified changes, is still to be determined. Nevertheless, our data provide strong support for the hypothesis that defects in the gene for the D-BP are responsible for the beta-oxidation defect in patients belonging to the BP CG.

Conjugation reactions catalyzed by bifunctional proteins related to beta-oxidation in bile acid biosynthesis

The conjugation reactions of hydration and dehydrogenation catalyzed by the dehydratase and dehydrogenase activities of D-3-hydroxyacyl-CoA dehydratase/D-3-hydroxyacyl-CoA dehydrogenase bifunctional protein (DBP) and enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase bifunctional protein (LBP) in the side chain degradation step of bile acid biosynthesis were investigated using chemically synthesized C27-bile acid CoA esters as substrates. The hydration catalyzed by DBP showed high diastereoselectivity for (24E)-3alpha,7alpha,12alpha-trihydroxy- and (24E)-3alpha,7alpha-dihydroxy-5beta-cholest-24-en-26-oyl CoA to give (24R,25R)-3alpha,7alpha,12alpha,24-tetrahydroxy- and (24R,25R)-3alpha,7alpha,24-trihydroxy-5beta-cholestan-26-oyl CoAs, respectively, and the dehydrogenation catalyzed by DBP also showed high stereospecificity for the above (24R,25R)-isomers to give 3alpha,7alpha,12alpha-trihydroxy- and 3alpha,7alpha-dihydroxy-24-oxo-5beta-cholestan-26-oyl CoAs, respectively. On the other hand, the dehydratase activity of LBP displayed a different diastereoselectivity producing the (24S,25S)-isomer, and dehydrogenase activity of LBP was stereospecific for the (24S,25R)-isomer to give the above 24-oxo-derivative. The hydration and dehydrogenation reactions catalyzed by DBP were effectively conjugated to convert (24E)-5beta-cholestenoyl CoA to 24-oxo-5beta-cholestanoyl CoA. However, the reactions catalyzed by LBP were not conjugated. These results indicate that DBP plays an important role in the biosynthesis of bile acid.

Molecular basis of D-bifunctional protein deficiency

Peroxisomal disorders appear with a frequency of 1:5000 in newborns. They are caused either by peroxisomal assembly defects or by deficiencies of single peroxisomal enzymes. The phenotypes vary widely: affected humans may die very early in life within a few days to several months as a result of the impairment in essential peroxisomal functions as, for example, in Zellweger syndrome, or they may show only minor disabilities as is in acatalasemia. The deficiency of D-bifunctional protein, an enzyme involved in peroxisomal beta-oxidation of certain fatty acids and the synthesis of bile acids, causes a very severe, Zellweger-like phenotype. A number of different mutations in the gene coding for the enzyme were found in humans causing the total or partial loss of its enzymatic function. This paper gives a review of cases and their molecular basis.

Gene expression of peroxisomal beta-oxidation enzymes in rat brain

Despite increasing insight into peroxisomal beta-oxidation, it is still not clear which enzymes catalyze very-long-chain fatty acid degradation. Using the northern blot and RT-PCR techniques, a brain-specific expression is demonstrated for acyl-CoA oxidase 3II mRNA, thiolase-A and trans2,3enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase multifunctional enzyme type 2.

Functional heterogeneity of C-terminal peroxisome targeting signal 1 in PEX5-defective patients

To investigate mechanisms related to functions of the peroxisome targeting signal (PTS) 1 receptor, Pex5p, we analyzed peroxisome matrix protein import in fibroblasts from three patients with peroxisome biogenesis disorders, all with different mutations in the PEX5 gene. The patients 2-01 (Zellweger syndrome) and 2-05 (neonatal adrenoleukodystrophy) have the reported mutations, R390X and N489K, and patient 2-03 (infantile Refsum disease) has a newly identified mutation, S563W. Fibroblasts from 2-03 (S563W) were detected in both PTS1 and PTS2 imports despite the PEX5 defect, findings in contrast with fibroblasts from 2-05 (N489K) severely defective in PTS1 import and those from 2-01 (R390X) severely defective in both PTS1 and PTS2. The PTS1 receptor in 2-03 is functional for only the C-terminal -SKL sequence (acyl-CoA oxidase) and had little or no function for C-terminal -AKL (D-bifunctional protein and sterol carrier protein 2) and -KANL (catalase) sequences, respectively. After transfection of these mutated PEX5 cDNA into the PEX5-defective CHO mutant, transformants of ZP102 revealed that each mutation was responsible for each dysfunction of the PTS1 import. It seems apparent that -AKL and -KANL are poorer variants of PTS1 and are likely to be more susceptible to effects of mutation of its receptor, Pex5p.

A novel peroxisomal enzyme, D-3-hydroxyacyl-CoA dehydratase/D-3-hydroxyacyl-CoA dehydrogenase bifunctional protein: its expression in the developing human brain

D-bifunctional protein, which is a newly recognized peroxisomal enzyme (D-3-hydroxyacyl-CoA dehydratase/D-3-hydroxyacyl-CoA dehydrogenase), demonstrates a characteristic development of pattern in the human brain. At 13 gestational weeks (GW), D-bifunctional protein immunoreactivity first appeared in the brain. Each neuron exhibited increased immunoreactivity along with growth in size as age increased and size with age. Glial cells in the white matter showed immunoreactivity after 30 GW. On the other hand, the L-bifunctional protein immunoreactivity was reported in neurons from 23 or 25 GW and in the white matter from 12 or 14 GW. Because of polymicrogyria in conditions such as infantile Refsum disease and infantile adrenoleukodystrophy, peroxisomal enzymes are thought to play an important role in neuronal migration and possibly myelination. D-bifunctional protein may be relevant to neuronal migration and L-bifunctional protein may be involved in axonal growth and synaptic development. This study is designed to access the ontogeny of D-bifunctional protein in the human brain.

Prenatal diagnosis of peroxisomal D-3-hydroxyacyl-CoA dehydratase/D-3-hydroxyacyl-CoA dehydrogenase bifunctional protein deficiency

The prenatal diagnosis of peroxisomal D-3-hydroxyacyl-coenzyme A (CoA) dehydratase/D-3-hydroxyacyl-CoA dehydrogenase bifunctional protein (D-BP) deficiency was performed by peroxisomal beta-oxidation assay, indirect immunofluorescence staining, immunoblot analysis, and gene analysis of cultured amniocytes obtained from a fetus at 16 weeks' gestational age. beta-Oxidation activity, measured by [1-14C] lignoceric acid oxidation, was markedly decreased compared with the controls. Large peroxisomes were readily identified by immunofluorescence staining with anti-human catalase, as was found in the reported patients. Immunoreactive D-BP material was absent on immunoblot analysis and immunofluorescence staining with anti-human D-BP. Reverse transcriptase polymerase chain reaction (RT-PCR) analysis revealed the presence of the same 237-bp deletion in the cDNA as that detected in a sibling (the proband). The autopsied fetus showed the characteristic facial appearance and D-BP was deficient on immunoblot and immunohistopathological studies of the fetal tissues. No neuronal migration disorder was identified. This seems to be the first prenatal diagnosis of D-BP deficiency.

Characterization of the HSD17B4 gene: D-specific multifunctional protein 2/17beta-hydroxysteroid dehydrogenase IV

The HSD17B4 gene codes for a 80 kDa multifunctional enzyme containing three distinct functional domains and is localized in peroxisomes. The N-terminal part exhibits 3-hydroxyacyl-CoA dehydrogenase and 17beta-hydroxysteroid dehydrogenase activity whereas the central part shows enoyl-CoA hydratase activity. The carboxy-terminal part of the protein has sterol-carrier-protein activity. The protein is widely expressed, however in several tissues like brain, uterus and lung its expression is limited to specific cells like Purkinje cells or luminal epithelium. The HSD17B4 gene consist of 24 exons and 23 introns with classical intron-exon junctions spanning more than 100 kbp. The importance of the HSD17B4 protein is stressed by the identification of patients with severe clinical abnormalities due to mutations in the HSD17B4 gene. We have now checked the consequences of one frequent mutation, G16 S, which results in inactivation of the enzyme due to loss of interaction with NAD+.

Peroxisomal bifunctional protein deficiency revisited: resolution of its true enzymatic and molecular basis

In the past few years, many patients have been described who have a defect of unknown origin in the peroxisomal beta-oxidation pathway. Complementation analysis has been done by various groups to establish the extent of the genetic heterogeneity among the patients. These studies were based on the use of two established cell lines, one with a deficiency of acyl-CoA oxidase and one with a deficiency of l-bifunctional protein (l-BP), and they showed that most patients belong to the l-BP-deficient group. However, molecular analysis of the cDNA encoding l-BP in patients failed to show any mutations. The recent identification of a new d-specific bifunctional protein (d-BP) prompted us to reinvestigate the original patient with presumed l-BP deficiency. In a collaborative effort, we have now found that the true defect in this patient is at the level of the d-BP and not at the level of the l-BP. Our results suggest that most, if not all, patients whose condition has been diagnosed as l-BP are, in fact, d-BP deficient. We tested this hypothesis in nine patients whose condition was diagnosed as l-BP deficiency on the basis of complementation analysis and found clear-cut mutations in the d-BP cDNA from all patients.

Structure of the gene for the human 17beta-hydroxysteroid dehydrogenase type IV

The 17beta-hydroxysteroid dehydrogenase type IV (17beta-HSD IV) is a multifunctional enzyme that is localized in the peroxisomes. The N-terminal part has dehydrogenase activity, the central part has hydratase activity, and the carboxy-terminal part is responsible for sterol transport. Recent observations of mutations in the human 17beta-HSD IV cDNA leading to a severe peroxisomal disorder motivated us to define the genomic organization of this gene mapped to Chromosome (Chr) 5q2. We show here that this gene consist of 24 exons and 23 introns with classical intron-exon junctions spanning more than 100 kbp. By mapping the regulatory region of this gene, we have shown that the first 400 bp upstream of the transcription start site are sufficient to activate transcription. The data presented here will permit sequence analysis of patients with peroxisomal disorders.

17Beta-hydroxysteroid dehydrogenases in human bone cells

Interconversion of estrogens by osteoblasts may play a role in regulating bone mass. As a first step toward exploring this possibility, we investigated the expression and activity of 17beta-hydroxysteroid dehydrogenases (17beta-HSDs) in cultured human osteoblasts (HOB) and osteoblast-like osteosarcoma cells (MG63, TE85, and SaOS-2). Significant 17beta-HSD activity was detected in cell-free extracts of all bone cells with oxidation of estradiol to estrone predominating over reduction. Reverse transcription-polymerase chain reaction (RT-PCR) experiments showed that the mRNA for 17beta-HSD I was detectable only in MG63 cells, albeit at low levels, while 17beta-HSD II was present in MG63, TE85, and HOB, but not SaOS-2, and 17beta-HSD III was absent from each bone cell type. 17Beta-HSD IV was the only isoform present in all bone cells analyzed. Further analysis of the expression of 17beta-HSD IV in these bone cells by immunoblotting revealed both the full-length 83 kDa protein and the proteolytic 38 kDa form. The kinetic parameters for estradiol oxidation by purified recombinant 17beta-HSD IV (Km = 49.7 microM, Vmax = 79.4 nmol/minute/mg of protein) and its HSD-domain (Km = 79.4 microM, Vmax = 476 nmol/minute/mg of protein) were significantly higher than previously reported, but consistent with the values obtained with crude cell-free extracts of SaOS-2 cells (Km = 98.8 microM, Vmax = 0.07 nmol/minute/mg of protein) which contain only 17beta-HSD IV based on RT-PCR. These studies show that bone cells have the capacity to interconvert circulating estrogens and suggest that bone cell 17beta-HSDs serve primarily to attenuate the continuing actions of estradiol through conversion to its less potent form, estrone, under certain conditions.

Peroxisomal D-hydroxyacyl-CoA dehydrogenase deficiency: resolution of the enzyme defect and its molecular basis in bifunctional protein deficiency

Peroxisomes play an essential role in a number of different metabolic pathways, including the beta-oxidation of a distinct set of fatty acids and fatty acid derivatives. The importance of the peroxisomal beta-oxidation system in humans is made apparent by the existence of a group of inherited diseases in which peroxisomal beta-oxidation is impaired. This includes X-linked adrenoleukodystrophy and other disorders with a defined defect. On the other hand, many patients have been described with a defect in peroxisomal beta-oxidation of unknown etiology. Resolution of the defects in these patients requires the elucidation of the enzymatic organization of the peroxisomal beta-oxidation system. Importantly, a new peroxisomal beta-oxidation enzyme was recently described called D-bifunctional protein with enoyl-CoA hydratase and 3-hydroxyacyl-CoA dehydrogenase activity primarily reacting with alpha-methyl fatty acids like pristanic acid and di- and trihydroxycholestanoic acid. In this patient we describe the first case of D-bifunctional protein deficiency as resolved by enzyme activity measurements and mutation analysis. The mutation found (Gly16Ser) is in the dehydrogenase coding part of the gene in an important loop of the Rossman fold forming the NAD+-binding site. The results show that the newly identified D-bifunctional protein plays an essential role in the peroxisomal beta-oxidation pathway that cannot be compensated for by the L-specific bifunctional protein.

Thiolase involved in bile acid formation

The formation of cholic acid and chenodeoxycholic acid through cleavage of the side chains of CoA esters of 3alpha,7alpha,12alpha-trihydroxy-5beta-choles tan-26-oic acid and 3alpha,7alpha-dihydroxy-5beta-cholestan-26-oic acid is believed to occur in peroxisomes. Recently, we found a new peroxisomal enzyme, D-3-hydroxyacyl-CoA dehydratase/D-3-hydroxyacyl-CoA dehydrogenase bifunctional protein, and suggested that this bifunctional protein is responsible for the conversion of 3alpha,7alpha,12alpha-trihydroxy-5beta-cholest-2 4-en-26-oyl-CoA and 3alpha,7alpha-dihydroxy-5beta-cholest-24-en-26-oyl-CoA to their 24-oxo-forms. In the present study, the products of this bifunctional protein reaction were analyzed by gas chromatography-mass spectrometry, and the formation of 24-oxo-27-nor-cholestanes was confirmed. Previously, we found a new thiolase in Caenorhabditis elegans, P-44, and suggested that P-44 and sterol carrier protein x, a peroxisomal protein, constitute a second group of 3-oxoacyl-CoA thiolases. The production of cholic acid and chenodeoxycholic acid from the precursors on incubation with the bifunctional protein and sterol carrier protein x or P-44 was confirmed by gas chromatography.

Bile acid profiles in a peroxisomal D-3-hydroxyacyl-CoA dehydratase/D-3-hydroxyacyl-CoA dehydrogenase bifunctional protein deficiency

Bile acid profiles in serum, urine and bile from an infant with a peroxisomal D-3-hydroxyacyl-CoA dehydratase/D-3-hydroxyacyl-CoA dehydrogenase bifunctional protein (D-bifunctional protein) deficiency were analyzed by means of gas-liquid chromatography, gas-liquid chromatography-mass spectrometry, and high-performance liquid chromatography. As in such several peroxisomal disorders as Zellweger syndrome, neonatal adrenoleukodystrophy, and infantile Refsum disease, the accumulation of C27-bile acid intermediates was also demonstrated in the infant with D-bifunctional protein deficiency, accounting for 74% of the total bile acids in serum, 59% in urine, and 35% in bile. In addition, the major constituents of the C27-bile acids were (24R,25R)- and (24R,25S)-3alpha,7alpha,12alpha,24-tetrahydroxy-5be ta-cholestanoic acids along with small amounts of their 24S counterparts. Since immunoreactive acyl-CoA oxidase, L-bifunctional protein, and thiolase were all present in the liver, the impairment of the oxidative side-chain cleavage in bile acid biosynthesis is considered to be due to the defect of D-bifunctional protein.

The human peroxisomal multifunctional protein involved in bile acid synthesis: activity measurement, deficiency in Zellweger syndrome and chromosome mapping

The dehydrogenation of 24R,25R-varanoyl-CoA, the physiological intermediate formed during the peroxisomal breakdown of the bile acid intermediate trihydroxycoprostanic acid, was studied in human liver. The reaction appeared to be catalyzed by two different enzymes. A first one, present in the cytosol, did not discriminate between the four possible varanoyl-CoA isomers and did not require the CoA moiety. The second enzymic activity was associated with peroxisomes and acted only on the 24R,25R-isomer, in which the 24-hydroxy group possesses the D-configuration. The D-specific dehydrogenase is part of a 79 kDa protein which represents the human counterpart of a recently discovered second multifunctional protein in rat liver peroxisomes, named multifunctional protein 2 (MFP-2). Human MFP-2, like its rat counterpart, is also responsible for the formation (by hydratation) of 24R,25R-varanoyl-CoA. A deficiency of MFP-2 in Zellweger liver could be demonstrated immunologically by using antibodies against the rat enzyme and enzymically -- after removal of the cytosol -- by using 24R,25R-varanoyl-CoA. The gene coding for MFP-2 was mapped to chromosome 5q2.3.

Expression of 17 beta-hydroxysteroid dehydrogenase type IV in chick retinal pigment epithelium

Retinal pigment epithelium (RPE) has essential roles that maintain functions of the neural retina. Previously, we described that the 3b5 monoclonal antibody (3b5 mAb) recognized the RPE cells in the chick embryonic eye. In the present study, a gene coding for the 3b5 antigen has been cloned and sequenced. A 10-day-old embryonic RPE cDNA library was constructed in lambda Uni-ZAP XR, and screened with the 3b5 mAb as a probe. The complete nucleotide sequence of the antigen recognized by the 3b5 mAb was obtained. The cDNA encodes a 735 amino acid protein with a calculated molecular mass of 80,147 Da. The deduced amino acid sequence shares 72% identity with the human 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) type IV. Northern blot analysis detected a 2.9 kb transcript. Immunohistochemical and in-situ hybridization studies revealed that 17 beta-HSD type IV was preferentially expressed in the RPE cells. The expression of steroid metabolizing enzymes in the RPE cells is able to create estrogenic environment, which may have a role of maintenance of the neural retina.

Local estradiol metabolism in osteoblast- and osteoclast-like cells

Bone is an estradiol-responsive tissue. Estrogen withdrawal during the menopause causes loss of bone mass and clinically relevant osteoporosis in a third of all women. Sufficient or impaired local production, as well as degradation of estradiol in cells present in the bone microenvironment might be an important mechanism of rescue or might contribute to the development of osteoporosis, respectively. We therefore investigated aromatase and 17beta-hydroxysteroid dehydrogenase type IV (17beta-HSD IV) expression in osteoblast- and osteoclast-like cells. Aromatase mRNA was increasingly expressed in myeloid THP 1 cells differentiated along the monocyte/phagocyte pathway exploiting vitamin D and either granulocyte-macrophage-stimulating factor (GMCSF) or macrophage-stimulating factor (MCSF). In long-term cultures, when sequentially exposed to vitamin D (days 0-21) and GMCSF (days 5-10) and plated on collagen, the amount of expression of aromatase mRNA steadily increased along with the increasing expression of osteopontin mRNA, alpha(v) integrin mRNA, c-fms (MCSF-receptor) mRNA and multinucleated cells developing. The conversion of estradiol from testosterone (10(-7) M/l) in the supernatants of dishes mirrored changes in aromatase mRNA expression and by day 21 rose to 30,000 ng/10(7) cells/24 h. 17Beta-HSD IV mRNA expression was abundant in undifferentiated THP 1 cells and was decreased to approximately 50% by day 21. Unstimulated SV-40 immortalized fetal osteoblasts did not express aromatase mRNA, but the expression was stimulated by the addition of the phorbol ester phorbol myristate acetate (PMA). Unstimulated osteoblasts from primary cultures did not express aromatase mRNA. Osteoblast-like osteosarcoma cells MG 63 expressed faint levels of aromatase mRNA in contrast to the osteosarcoma cell line HOS 58. 17Beta-HSD IV mRNA was expressed in fetal osteoblasts as well as in osteoblasts from primary culture, MG 63 and HOS 58 cells. In summary, we can show the expression of estradiol metabolizing enzymes in cells which are present in the bone microenvironment. Impaired aromatase expression and/or enhanced expression of 17beta-HSD IV may contribute to the pathogenesis of osteoporosis.

Physiological role of D-3-hydroxyacyl-CoA dehydratase/D-3-hydroxyacyl-CoA dehydrogenase bifunctional protein

The second and third reactions of the peroxisomal beta-oxidation spiral are thought to be catalyzed by enoyl-CoA hydratase/L-3-hydroxyacyl-CoA dehydrogenase bifunctional protein (L-bifunctional protein). Recently, we found the presence of D-3-hydroxyacyl-CoA dehydratase/D-3-hydroxyacyl-CoA dehydrogenase bifunctional protein (D-bifunctional protein) in mammalian peroxisomes. Therefore, we studied the physiological role of the D-bifunctional protein. The contents of the L- and D-bifunctional proteins were about 0.01 and 0.5 microg/mg protein, respectively, in cultured human skin fibroblasts. The activity of conversion of hexadecenoyl-CoA to 3-ketopalmitoyl-CoA by the D-bifunctional protein was estimated to be about 0.5 milliunit/mg of fibroblast protein. This value was about 100-fold that of the L-bifunctional protein in the fibroblasts. From comparison of the activities of the bifunctional proteins with the rate of palmitate oxidation and the activities of acyl-CoA oxidase and 3-ketoacyl-CoA thiolase, it is proposed that the D-bifunctional protein plays a major role in the peroxisomal oxidation of palmitate in the fibroblasts. The contents of both the L- and D-bifunctional proteins in liver were about 2.5 microg/mg protein. Therefore, it is suggested that the D-bifunctional protein also plays a significant role in human liver peroxisomal fatty acid oxidation. Actions of the bifunctional proteins on enoyl forms of other acyl-CoA derivatives were examined. The D-bifunctional protein but not the L-bifunctional protein reacted with 2-methylhexadecenoyl-CoA and 3alpha,7alpha,12alpha-trihydroxy-5beta-cholest-2 4-enoyl-CoA. We propose that, among the reactions of the distinct group of carboxylates oxidized specifically in peroxisomes, oxidation of 2-methyl-branched fatty acids and side-chain shortening of cholesterol for bile acid formation are catalyzed by the D-bifunctional protein, but not the L-bifunctional protein.

Structure of D-3-hydroxyacyl-CoA dehydratase/D-3-hydroxyacyl-CoA dehydrogenase bifunctional protein

When D-3-hydroxyacyl-CoA dehydratase/D-3-hydroxyacyl-CoA dehydrogenase bifunctional protein was purified from human liver, two preparations were obtained. One contained a 77-kDa polypeptides as the main and minor smaller polypeptides including a 46-kDa polypeptide, and this preparation showed both the dehydratase and dehydrogenase activities. The other preparation was a homodimer of the 46-kDa polypeptide and showed only the dehydratase activity. Further analysis indicated that the native enzyme is a homodimer of 77-kDa polypeptide, which was proteolytically modified during purification. The cDNA for the human 77-kDa polypeptide was cloned. The amino acid sequences of the peptides derived from the components of the enzyme preparations were located in the deduced amino acid sequence of the cDNA. The preparation containing the 77-kDa polypeptide was treated with a protease, and two monofunctional fragments were separated. The dehydrogenase and dehydratase fragments were located on the amino- and carboxyl-terminal sides, respectively, of the deduced amino acid sequence of the cDNA. The protein expressed by the cDNA with the entire coding region exhibited both the dehydratase and dehydrogenase activities, and that expressed by a truncated version covering the carboxyl-terminal side exhibited only the dehydratase activity. The cloned cDNA was identical to the human 17 beta-hydroxysteroid dehydrogenase IV cDNA.

Peroxisome proliferators alter the expression of estrogen-metabolizing enzymes

Exposure to some peroxisome proliferator chemicals (PPC) leads to toxic effects on sex organ function possibly by alterations of steroid hormone metabolism. A systematic search for genes whose mRNA levels are modulated by the PPC WY-14643 (WY) was carried out in rat liver, a site of steroid hormone metabolism. The sequence of one up-regulated cDNA (2480 bp) was predicted to encode a protein of 735 amino acids with 82% identity to the porcine 17 beta-hydroxysteroid dehydrogenase type IV (HSD IV) originally isolated as a 17 beta-estradiol dehydrogenase. The rat HSD IV was localized to peroxisomes and was regulated by diverse PPC by two distinct mechanisms. Induction of HSD IV and acyl-CoA oxidase (ACO) proteins in rat liver at different treatment times and concentrations of gemfibrozil (GEM) and di-n-butyl phthalate (DBP) were almost identical, suggesting that HSD IV mRNA induction involves the peroxisome proliferator-activated receptor alpha, a regulator of ACO. In contrast, HSD IV protein levels were only weakly induced by WY, a strong inducer of ACO protein, even though the levels of both HSD IV and ACO mRNA were strongly stimulated by WY. Thus HSD IV protein levels were uniquely regulated pretranslationally by WY. In addition to HSD IV we also identified the male-specific alpha 2u-globulin as a PPC down-regulated gene. This prompted us to examine the expression of another male-specific gene, CYP2C11, that catalyzes the hydroxylations of estradiol at the 2 and 16 alpha positions. Cyp2C11 protein expression in rat liver was either decreased or completely abolished after a 3-week treatment by GEM or WY, respectively. Decreased expression of enzymes which inactivate estradiol including Cyp2C11, and the reported increased expression of aromatase may explain why male rats exposed to diverse PPC have higher serum estradiol levels. These higher estradiol levels in male rats have been thought to be mechanistically linked to Leydig cell hyperplasia and adenomas. Increased conversion of estradiol to the less active estrone by HSD IV induction may explain how exposure to the phthalate di-(2-ethylhexyl) phthalate leads to decreases in serum estradiol levels and suppression of ovulation in female rats.

The key role of 17 beta-hydroxysteroid dehydrogenases in sex steroid biology

17 beta-Hydroxysteroid dehydrogenase (17 beta-HSD) controls the last step in the formation of all androgens and all estrogens. This crucial role of 17 beta-HSD is performed by at least five 17 beta-HSD isoenzymes having individual cell-specific expression, substrate specificity, regulation mechanisms, and reductive or oxidative catalytic activity. Both estrogenic and androgenic 17 beta-HSD activities were found in all 25 rhesus monkey and 15 human peripheral intracrine tissues examined. Type 1 17 beta-HSD is a protein of 327 amino acids catalyzing the formation of 17 beta-estradiol from estrone. Its x-ray structure was the first to be determined among mammalian steroidogenic enzymes. Initially crystallized with NAD, the crystal structure of type 1 17 beta-HSD has just been determined as a complex with 17 beta-estradiol, thereby illustrating the conformation of the substrate-binding site. Type 2 17 beta-HSD degrades 17 beta-estradiol into estrone and testosterone into androstenedione, and type 4 17 beta-HSD mainly degrades 17 beta-estradiol into estrone and androst-5-ene-3 beta, 17 beta-diol into dehydroepiandrosterone. Types 3 and 5 17 beta-HSD, on the other hand, catalyze the formation of testosterone from androstenedione in the testis and peripheral tissues, respectively. The various types of human 17 beta-HSD, because of their tissue-specific expression and substrate specificity, provide each peripheral cell with the necessary mechanisms to control the level of intracellular androgens and/or estrogens, a new area of hormonal control that we call intracrinology.

Steroids, fatty acyl-CoA, and sterols are substrates of 80-kDa multifunctional protein

The 2.9-kb mRNA of 17 beta-hydroxysteroid dehydrogenase IV codes for an 80-kDa (737 amino acids) protein featuring domains that are not present in the other human 17 beta-hydroxysteroid dehydrogenases. The N-terminal part reveals conserved motifs of the short-chain alcohol dehydrogenase family. The central- and C-terminal domains are similar to peroxisomal enzymes for beta-oxidation of fatty acids and to sterol carrier protein 2. The 80-kDa protein is N-terminally cleaved to a 32-kDa fragment (amino acids 1-323). Both the 80-kDa and the N-terminal 32-kDa peptides are able to catalyze the dehydrogenation with steroids at the C17 position and with 3-hydroxyacyl-CoA. The central part of the 80-kDa protein (amino acids 324-596) catalyzes the 2-enoyl-acyl-CoA hydratase reaction with high efficiency. The C-terminal part of the 80-kDa protein (amino acids 597-737) facilitates the transfer of 7-dehydrocholesterol and phosphaidylcholine between membranes in vitro. The unique multidomain structure of the 80-kDa protein permits the catalysis of several reactions previously thought to be performed by complexes of different enzymes.

NATURE OF BUTYRATE OXIDATION BY MYCOPLASMA HOMINIS

VanDemark, P. J. (Cornell University, Ithaca, N.Y.), and P. F. Smith. Nature of butyrate oxidation by Mycoplasma hominis. J. Bacteriol. 89:373-377. 1965.-Cell-free extracts of butyrate - grown Mycoplasma hominis strain O7, though lacking thiokinase activity on butyric acid, were found to activate butyrate via an acetyl-butyric thiophorase. These extracts also contained an aceto-coenzyme A (CoA) kinase, a butyryl-CoA dehydrogenase, a crotonase, a reduced nicotinamide adenine dinucleotide-specific beta-hydroxybutyryl-CoA dehydrogenase, and a thiolase. Thiolase activity was stimulated by the addition of magnesium ions. The presence of these enzyme activities in this Mycoplasma species supports the hypothesis that a fatty acid oxidation represents an energy source for the nonfermentative pleuropneumonia-like organisms.

Purification and properties of rat D-3-hydroxyacyl-CoA dehydratase: D-3-hydroxyacyl-CoA dehydratase/D-3-hydroxyacyl-CoA dehydrogenase bifunctional protein

We have previously purified two D-3-hydroxyacyl-CoA dehydratase preparations from human liver. One preparation contained a 77-kDa polypeptide and smaller polypeptides, and the other was a homodimer of a 46-kDa polypeptide. Three different purified rat peroxisomal D-3-hydroxyacyl-CoA dehydratase preparations have been reported. Therefore, rat enzyme was purified in this study to confirm the enzyme structure. Two preparations with similar molecular structures to the human enzyme preparations were obtained, and these were similar to each other in immunochemical and catalytic properties. It was suggested that the native enzyme was a homodimer of the 77-kDa polypeptide, and this enzyme was modified to a homodimer of the 46-kDa polypeptide, because conversion of the 77-kDa polypeptide to smaller polypeptides including the 46-kDa polypeptide was clearly observed during purification. Rat liver subcellular fractionation study indicates that this enzyme is located in peroxisomes. The enzyme preparation containing the 77-kDa polypeptide catalyzed the D-3-hydroxyacyl-CoA dehydrogenase reaction as well as the dehydratase reaction. Thus, it is proposed that this enzyme is D-3-hydroxyacyl-CoA dehydratase/ D-3-hydroxyacyl-CoA dehydrogenase bifunctional protein.

Molecular characterization of mouse 17 beta-hydroxysteroid dehydrogenase IV

17 beta-hydroxysteroid dehydrogenases (17 beta-HSD) catalyze the conversion of estrogens and androgens at the C17 position. The 17 beta-HSD type I, II, III and IV share less than 25% amino acid similarity. The human and porcine 17 beta-HSD IV reveal a three-domain structure unknown among other dehydrogenases. The N-terminal domains resemble the short chain alcohol dehydrogenase family while the central parts are related to the C-terminal parts of enzymes involved in peroxisomal beta-oxidation of fatty acids and the C-terminal domains are similar to sterol carrier protein 2. We describe the cloning of the mouse 17 beta-HSD IV cDNA and the expression of its mRNA. A probe derived from the human 17 beta-HSD IV was used to isolate a 2.5 kb mouse cDNA encoding for a protein of 735 amino acids showing 85 and 81% similarity with human and porcine 17 beta-HSD IV, respectively. The calculated molecular mass of the mouse enzyme amounts to 79,524 Da. The mRNA for 17 beta-HSD IV is a single species of about 3 kb, present in a multitude of tissues and expressed at high levels in liver and kidney, and at low levels in brain and spleen. The cloning and molecular characterization of murine, human and porcine 17 beta-HSD IV adds to the complexity of steroid synthesis and metabolism. The multitude of enzymes acting at C17 might be necessary for a precise control of hormone levels.

Changing stereochemistry for a metabolic pathway in vivo. Experiments with the peroxisomal beta-oxidation in yeast

The biosphere is inherently built of chiral molecules, and once their metabolism is established, the stereochemical course of the reactions involved is seen to remain highly conserved. However, by replacing the yeast peroxisomal multifunctional enzyme (MFE), which catalyzes the second and third reactions of beta-oxidation of fatty acids via D-3-hydroxyacyl-CoA intermediates, with rat peroxisomal MFE, which catalyzes the same reactions via L-3-hydroxy intermediates, it was possible to change the chiralities of the intermediates in a major metabolic pathway in vivo. Both stereochemical alternatives allowed the yeast cells to grow on oleic acid, implying that when the beta-oxidation pathways evolved, the overall function was the determining factor for the acquisition of MFEs and not the stereospecificities of the reactions themselves.

Molecular cloning of a novel widely expressed human 80 kDa 17 beta-hydroxysteroid dehydrogenase IV

Reactions of oestrogens and androgens at position C-17 are catalysed by 17 beta-hydroxysteroid dehydrogenases (17 beta-HSDs). Cloning of the cDNA of a novel human 17 beta-HSD IV and expression of its mRNA are described. A probe derived from the recently discovered porcine 17 beta-oestradiol dehydrogenase (17 beta-EDH) was used to isolate a 2.6 kb human cDNA encoding a continuous protein of 736 amino acids of high (84%) similarity to the porcine 17 beta-EDH. The calculated molecular mass of the human enzyme is 79,595 Da. Other sequence similarities shared by the two enzymes are: an N-terminal sequence which is similar to that of members of the short-chain alcohol dehydrogenase family; amino acids 343-607 which are similar to the C-terminal domains of a trifunctional Candida tropicalis enzyme and the FOX2 gene product of Saccharomyces cerevisiae; amino acids 596-736 which are similar to human sterol carrier protein 2. The previously cloned human 17 beta-HSD I, II and III are less than 25% identical with 17 beta-HSD IV. mRNA for HSD IV is a single species of 3.0 kb, present in many tissues with highest concentrations in liver, heart, prostate and testes. When over-expressed in mammalian cells, the human 17 beta-HSD IV enzyme displays a specific unidirectional oxidative 17 beta-HSD activity.

Fatty acid beta-oxidation in glyoxysomes. Characterization of a new tetrafunctional protein (MFP III)

We describe a new form of a multifunctional protein possessing the enzyme activities of delta 3, delta 2-enoyl-CoA isomerase, 3-hydroxyacyl-CoA epimerase, L-3-hydroxyacyl-CoA dehydrogenase and L-3-hydroxyacyl-CoA forming 2-trans-enoyl-CoA hydratase. This isoform, characterized by a molecular mass of 81 kDa and an isoelectric point above pH 9, was designated MFP III. Along with the tetrafunctional 76.5 kDa MFP II and the trifunctional 74 kDa MFP I, MFP III participates in degradation of fatty acid in glyoxysomes during mobilization of fat reserves. In combination with thiolase, MFP III encompasses all activities to degrade 3-cis-enoyl-CoAs to acetyl-CoA.

Peroxisomal multifunctional beta-oxidation protein of Saccharomyces cerevisiae. Molecular analysis of the fox2 gene and gene product

The gene encoding the multifunctional protein (MFP) of peroxisomal beta-oxidation in Saccharomyces cerevisiae was isolated from a genomic library via functional complementation of a fox2 mutant strain. The open reading frame consists of 2700 base pairs encoding a protein of 900 amino acids. The predicted molecular weight (98,759) is in close agreement with that of the isolated polypeptide (96,000). Analysis of the deduced amino acid sequence revealed similarity to the MFPs of two other fungi but not to that of rat peroxisomes or the multifunctional subunit of the Escherichia coli beta-oxidation complex. The FOX2 gene was overexpressed from a multicopy vector (YEp352) in S. cerevisiae and the gene product purified to apparent homogeneity. A truncated version of MFP lacking 271 carboxyl-terminal amino acids was also overexpressed and purified. Experiments to study the enzymatic properties of the wild-type MFP demonstrated an absence of activities originally assigned to an MFP of S. cerevisiae (crotonase, L-3-hydroxyacyl-CoA dehydrogenase, and 3-hydroxyacyl-CoA epimerase), whereas two other activities were found: 2-enoyl-CoA hydratase 2 (converting trans-2-enoyl-CoA to D-3-hydroxyacyl-CoA) and D-3-hydroxyacyl CoA dehydrogenase (converting D-3-hydroxyacyl-CoA to 3-ketoacyl-CoA). The truncated form contained only the D-3-hydroxyacyl-CoA dehydrogenase activity. These results clearly demonstrate that the beta-oxidation of fatty acids in S. cerevisiae follows a previously unknown stereochemical course, namely it occurs via a D-3-hydroxyacyl-CoA intermediate.

Enzymatic assay for 3-hydroxyacyl-CoA and 2-trans-enoyl-CoA intermediates of beta-oxidation

An enzymatic assay is presented for determining 3-hydroxyacyl-CoA and 2-trans-enoyl-CoA esters in tissue samples. The procedure includes extraction of acyl-CoA esters from frozen tissue samples with chloroform/methanol, stochiometric oxidation of the acyl esters to 3-keto-acyl-CoAs with 3-hydroxyacyl-CoA dehydrogenase in the presence or absence of enoyl-CoA hydratase, and an enzymatic cycling amplification of NADH produced for fluorometric determination. The procedure allows measurement of these intermediates of beta-oxidation at the picomole level. The method has been used successfully to measure the concentrations of 3-hydroxyacyl-CoA and 2-trans-enoyl-CoA esters in isolated rat hearts perfused with glucose or oleate or under anoxia.

A method for the preparation of 3-ketoacyl-CoA derivatives

A new method for the preparation of 3-ketoacyl-CoA thioesters (from malonylsemialdehyde to long-chain and phenylpropanoic 3-keto derivatives) is described. It utilizes the facile, thermodynamically very favorable, hydration of 2-alkynoyl-CoA thioesters by enoyl-CoA hydratase. The method is simple and avoids laborious organic syntheses or the use of multicomponent enzymatic methods.

The metabolic transformations of columbinic acid and the effect of topical application of the major metabolites on rat skin

The metabolism of columbinic acid by various fatty acid oxidizing enzyme systems was studied. A cyclooxygenase product, 9-hydroxy-(5E,10E,12Z)-octadecatrienoic acid, was formed nearly quantitatively by ram seminal vesicle microsomes and in small amounts by washed human platelets. The major lipoxygenase product from washed human platelets, soybean lipoxygenase, and neonatal rat epidermal homogenate was 13-hydroxy-(5E,9Z,11E)-octadecatrienoic acid, although lesser quantities of other isomers differing in the double bond configurations were also identified by ultraviolet spectrophotometry and gas chromatography-mass spectroscopy. Topical application of the major lipoxygenase product to paws of essential fatty acid-deficient rats resulted in nearly as complete resolution of the scaly dermatitis as did the application of columbinic acid itself; the cyclooxygenase product was not at all effective.

Evidence for a negative modulating effect of erucic acid on the peroxisomal beta-oxidation enzyme system and biogenesis in rat liver

In male rats fed a 30 cal% high-erucic acid (22:1 (13) (cis] rapeseed oil diet for 4 weeks a transient, small increase in peroxisomal beta-oxidation was observed in liver homogenates and isolated peroxisomes after approximately 1 week. Morphometric analysis revealed a progressive decrease in the average size of the liver peroxisomes (by approx. 20%), as well as their volume fraction (by more than 40%). A negative dose-response was observed when peroxisomal beta-oxidation was determined in animals fed rapeseed oil diets with a variable content of erucic acid. When erucic acid was given as subcutaneous injections the peroxisomal beta-oxidation decreased, in both liver homogenates and isolated peroxisomes. In contrast to recent proposals, our findings indicate that the amount of erucic acid cannot account for the small increase in peroxisomal beta-oxidation observed in the liver of rats adapted to a diet containing 30 cal% rapeseed oil with a high content of this fatty acid. In fact, by the selected criteria erucic acid seems to have a negative modulating effect on both the peroxisomal beta-oxidation enzyme system and biogenesis.