Autoantibodies of sera from patients with primary biliary cirrhosis recognize the alpha subunit of the decarboxylase component of human branched-chain 2-oxo acid dehydrogenase complex

BACKGROUND/AIMS

The major antigens for anti-mitochondrial autoantibodies in primary biliary cirrhosis (PBC) are the lipoyl-containing components of 2-oxo acid dehydrogenase complexes. Autoantibodies against the E1alpha subunit of the pyruvate dehydrogenase complex (PDH) also have been found, but those against the E1alpha subunit of branched-chain 2-oxo acid dehydrogenase complex (BCKADH) have not been detected. We investigated the occurrence of BCKADH-E1alpha-specific autoantibodies by employing the purified human antigen.

METHODS

The reactivities of PBC sera against purified antigens were assessed by ELISA and by immunoblotting analysis. The specificity of immunoreactivity was confirmed by absorption tests and affinity-purified antibodies.

RESULTS

Fourteen out of 27 PBC sera reacted with BCKADH-E1alpha, and these same sera also reacted with BCKADH-E2. No PBC sera reacted with BCKADH-E1beta. The reactivity of PBC sera with BCKADH-E1alpha was removed only when the sera were pre-absorbed with this antigen. However, reactivities to BCKADH-E2 and PDH-E1alpha were retained. Affinity-purified antibodies to BCKADH-E1alpha reacted with BCKADH-E1alpha, but not PDH-E1alpha. Thus, it was confirmed that anti-BCKADH-Elalpha did not cross-react with either BCKADH-E2 or PDH-E1alpha.

CONCLUSIONS

BCKADH-E1alpha-specific autoantibodies were found in the sera of PBC patients. The antibodies seem to occur subsequent to the anti-BCKADH-E2 antibody production, supporting the concept of intermolecular determinant spreading.

cDNA cloning of the chicken branched-chain alpha-keto acid dehydrogenase complex. Chicken-specific residues of the acyltransferase affect the overall activity and the interaction with the dehydrogenase

Branched-chain alpha-keto acid dehydrogenase complex is a macromolecule comprising three catalytic components: a dehydrogenase (E1) with alpha(2)beta(2) structure, an acyltransferase (E2) and a dihydrolipoamide dehydrogenase (E3). In the mammalian complex, the E2 component with 24 identical subunits forms a structural core, to which multiple copies of E1 and E3 bind noncovalently. We isolated cDNA clones encoding E1 alpha, E1 beta and E2 subunits from a chicken-liver cDNA library and performed nucleotide sequencing. Amino-acid sequences deduced from the nucleotide sequences revealed that chicken E1 alpha and E1 beta chains had substantially homologous sequences with the corresponding mammalian polypeptides, except for the N-terminus. Chicken E2 conserved three functional domains, a lipoyl-bearing domain, an E1/E3 binding domain and an inner-core domain, but contrasted strongly with mammalian E2 in respect of containing 11 additional residues in two interdomain linkers: nine sequential residues in one linker and two residues in the other. Replacement of many residues was also observed in the chicken linkers. When E2 activity for catalyzing the overall reaction was measured by activity reconstitution in combination with E1 and E3, chicken E2 was markedly less effective than mammalian E2. The capability of chicken E2 for binding E1 was also reduced when determined by the binding assay using sucrose density gradient centrifugation. Chicken E1 was functionally as well as structurally indistinguishable from mammalian E1. Thus the reduced catalytic activity of chicken E2 must arise from its reduced E1-binding capacity, which results from the characteristic structure of interdomain linkers in chicken E2.

VEGF-dependent signaling in retinal microvascular endothelial cells

We examined the effect of vascular endothelial growth factor (VEGF) on intracellular signal transduction pathways using isolated bovine microvascular endothelial cells (BREC). When cell growth was determined by [3H]thymidine incorporation, it was significantly stimulated by VEGF stimulation. In situ hybridization results also demonstrated that c-fos expression was enhanced by the stimulation. Although BREC expressed Flt-1 and Flk-1 as VEGF receptors at similar levels, VEGF stimulation preferentially enhanced the activity of Flt-1 tyrosine kinase. This stimulation initiated an increase in the level of GTP-form Ras and the activation of mitogen activated protein kinase (MAPK). On the other hand, BREC expressed the Janus kinase (Jak) family members Jak1, Jak2, and Tyk2, and the signal transducers and activators of transcription (Stat) family members Stat1, Stat3, and Stat6. These molecules were tyrosine phosphorylated under culture conditions used, and the phosphorylation of Tyk2 and Stat6 was specifically enhanced by VEGF stimulation. These results demonstrate that, in addition to Ras/MAPK pathways, the Flt-1/Tyk2/Stat6 pathway is important in VEGF signaling in BREC. These signal transduction systems may regulate the growth of retinal endothelial cells.

CpG motif-containing DNA fragments from sera of patients with systemic lupus erythematosus proliferate mononuclear cells in vitro

OBJECTIVE

To characterize DNA in sera of patients with systemic lupus erythematosus (SLE) in terms of size, guanine plus cytosine (G+C) content (by percentage), CpG dinucleotide (CpG) (percentage), and effects on mononuclear cells (MNC).

METHODS

Nine DNA clones were sequenced. Oligodeoxynucleotides with the characteristic CpG motif (TTCGAA or PuPuCGPyPy) were examined for their proliferative effect on MNC by [3H]thymidine incorporation, expression of HLA-DR and intercellular adhesion molecule (ICAM)-1 on monocytes by flow cytometry, and mRNA levels encoding interleukin 12 (IL-12) and interferon-gamma (IFN-gamma) by semiquantitative reverse transcription polymerase chain reaction.

RESULTS

The size of DNA clones ranged from 87 to 318 bp (mean +/- SD, 177+/-68) and enrichment in G+C and CpG ranged from 34.7 to 69.7% (48.1+/-10.7) and 0.63 to 12.8% (4.0+/-4.1), respectively. Three of 9 clones contained the characteristic CpG motif. Oligonucleotides proliferated MNC, and augmented HLA-DR and ICAM-1 expression in company with an increase of mRNA encoding IL-12 and IFN-gamma.

CONCLUSION

Circulating CpG motif-containing DNA fragments in SLE increased mRNA encoding IL-12 and IFN-gamma, which in turn increased HLA-DR and ICAM-1 on monocytes, resulting in MNC proliferation. This mechanism could contribute to the pathogenesis of SLE.

Effect of growth factors on expression of integrin subtypes in microvascular endothelial cells isolated from bovine retinas

We isolated microvascular endothelial cells from bovine retinas (BREC) by a colony isolation method, and investigated the effects of basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) on growth as well as integrin subtype expression of the cultured BREC. Either of the growth factors stimulated growth of the cultured BREC. In non-stimulated BREC, alpha v beta 3 integrin expression was predominant over the other integrin subtypes tested (alpha v beta 5, alpha 2 beta 1 and alpha 5 beta 1), but no enhancement of the alpha v beta 3 expression occurred by either growth factor stimulation. On the other hand, bFGF addition stimulated alpha v beta 5 and alpha 5 beta 1 expression while VEGF induced the alpha 2 beta 1 expression as well. These results suggest that external stimuli such as bFGF and VEGF alter integrin expression profiles of BREC and probably influence interactions of endothelial cells with extracellular matrix during angiogenesis which must be involved in pathogenesis of ischemic retinal disorders. In this respect, this BREC culture system could be useful to study the mechanism of neovascularization in these disorders.

Nucleotide sequence of the promoter region of chicken cytosolic phosphoenolpyruvate carboxykinase gene

The nucleotide sequence of the promoter region and its flanking regions which span - 1855 to +2083 in the chicken cytosolic phosphoenolpyruvate carboxykinase gene was determined. The transcription initiation site was located at 119 nucleotides downstream of the previously reported chicken kidney transcription initiation site of this gene. The nucleotide sequences of exons 1, 2, and 3 were highly homologous to the corresponding exons of the rat gene. Homology of the sequence - 1 to - 500 to that of rat gene was 52% and most of the hormone-responsive sequences in rat gene, such as the glucocorticoid-responsive region, were not conserved in the chicken gene, in accord with the species-specific responsiveness to starvation. In contrast, in the region of - 1 to - 300, some sequence motifs conserved both in the chicken and rat genes were found at essentially the same positions in the promoters. Such sequence motifs included a cAMP-responsive element (CRE), a nuclear factor-1 (NF-1/CTF)-binding site, and a hepatocyte nuclear factor-1 (HNF-1)-binding site. Transient expression of the reporter luciferase gene ligated to the 3' end of this chicken sequence (-1855 to +7) was observed in a primary culture of chick hepatocytes when dibutyryl cyclic AMP was added to the culture medium.

Antibodies to E1 and E2/Protein X components of pyruvate dehydrogenase complex in sera of patients with primary biliary cirrhosis

AIMS/METHODS

Using purified E1 component of pyruvate dehydrogenase complex (PDC) from bovine heart, we measured the levels of anti-E1 antibodies in PBC sera using ELISA and determined the degree of inhibition that these antibodies exerted on E1 enzyme activity. We also estimated levels of anti-E2/Protein X (Pro-X) antibodies in PBC sera using purified E2 and Pro-X of PDC which were copurified with E1.

RESULTS/CONCLUSIONS

Anti-E1 antibodies were detected in 87.5% (35/40) of PBC sera. Some of these sera inhibited E1 enzyme activity but inhibition did not correlate with levels of anti-E1 antibodies. A high positive correlation (r = 0.918) was found between levels of anti-E1 and anti-E2/Pro-X antibodies, suggesting that anti-PDC antibody production was stimulated by PDC itself. Levels of IgG class anti-E2/Pro-X antibodies were significantly higher in sera of symptomatic PBC patients than in those of asymptomatic PBC patients. It was also found that patients who were positive for only IgM class anti-E2/Pro-X antibodies had early-stage PBC.

Comparison of kinetic property between human seminal and renal gamma-glutamyltransferase

The initial-velocity kinetics, optimal pH, acceptor specificity and the influence of metal ions, EDTA and urea were studied on the human seminal gamma-glytamyltransferase (GGT) in comparison with the human renal GGT. The activity was measured with glycylglycine as an acceptor and with gamma-glutamyl-4-nitroanilide or gamma-glutamyl-3-carboxy-4-nitroanilide as a donor. Because the double-reciprocal plots showed paralled lines, the reaction of seminal GGT proceeds in nonsequence (Ping Pong Bi Bi) mechanism. The acceptor Michaelis constants for the seminal GGT were about 2 times higher than those for the renal enzyme with gamma-glutamyl-3-carboxy-4-nitroanilide as well as gamma-glutamyl-4-nitroanilide as donors, which the donor michaelis constants for seminal GGT were very similar to those for renal enzyme. The optimal pH and pK values were 8.2-8.6 and about 7.7, respectively. There was little difference in the specificity for various acceptors between the seminal and renal enzyme. Glycylglycylglycine was an effective acceptor other than glycylglycine, showing 80% of the activity with glycylgycine. Various substrates including metal ions tested were practically neither inhibitory nor stimulatory for seminal and renal GGTs.

Binding properties of the components of branched-chain 2-oxo acid dehydrogenase complex on ELISA

Binding characteristics among three catalytic components of rat liver branched-chain 2-oxo acid dehydrogenase complex (BCKADH) were investigated by ELISA. Dihydrolipoamide dehydrogenase (E3) was bound to solid-phase dihydrolipoamide acyltransferase (E2). The binding curve was hyperbolic giving a calculated half-maximal binding concentration of 167 ng/ml for E3. Specificity of the binding of E3 to E2 was certified by a competition experiment measuring binding of biotin-labeled E3 in the presence of unlabeled E3. The decarboxylase component (E1), which is the other catalytic component of the complex, prevented the E3 binding to E2. The specific binding between E2 and E3 was verified in the opposite direction with immobilized E3. E2 also bound to solid-phase E1 in a specific manner, and addition of E3 prevented the E2 binding to E1. No binding between E1 and E3 was observed. Thus, E1 and E3 prevented each other's binding to E2, suggesting that E1 and E3 may recognize overlapped binding sites on the E2 polypeptide or that they may, at least in part, sterically interact with each other on their binding to E2. The reconstitution experiment of the complex also supported such a mutually exclusive binding of E1 and E3 to the E2 core.

Differential processing of human and rat E1 alpha precursors of the branched-chain alpha-keto acid dehydrogenase complex caused by an N-terminal proline in the rat sequence

The N-terminal sequences of the E1 alpha, E1 beta and E2 subunits of the human branched-chain alpha-keto acid dehydrogenase complex have been determined by microsequencing. The N-terminal of human E1 beta and E2 subunits (Val and Gly, respectively) are identical to those of the corresponding rat and bovine subunits. However, the N-terminus of the human E1 alpha subunit (Ser) is identical to bovine, but differs from the rat E1 alpha (Phe) subunit. Comparison of the N-terminal sequences of human and rat E1 alpha subunits shows that the serine residue at the +1 position in the human sequence is replaced by a proline residue in the rat sequence. The presence of the proline residue apparently causes a 5'-shift by one residue in the cleavage site by the mitochondrial processing peptidase in the rat sequence, when compared to the human sequence. The results provide evidence that the mitochondrial processing peptidase cannot cleave an X-Pro bond, similar to trypsin, chymotrypsin and microsomal signal peptidases.

The source of the oxygen atom in the alpha-hydroxyglycine intermediate of the peptidylglycine alpha-amidating reaction

Peptidylglycine alpha-amidating activity catalyses the oxidation of a C-terminally glycine-extended peptide to a desglycine alpha-amidated peptide at the expense of ascorbate and O2 in the presence of Cu2+. The reaction involves oxidative N-dealkylation within the terminal glycine residue, with retention of the glycine N atom and release of the remainder as glyoxylate. Recent studies by us and others have revealed that the reaction consists of two steps via a carbinolamide as an intermediate (peptidyl alpha-hydroxyglycine), and also that two separate enzymes derived from a common precursor protein catalyse these steps, formation of the carbinolamide and its conversion into alpha-amide and glyoxylate. As for the mechanism of carbinolamide formation, two distinct pathways can be considered: direct mono-oxygenation at the glycine alpha-C atom and dehydrogenation leading to an imine followed by hydration. To draw a distinction between them, we carried out the reaction with D-Tyr-Val-Gly as the substrate either in the H2(18)O-enriched medium or under an atmosphere of 18O2, and isolated the alpha-hydroxylglycine intermediate. The fast-atom-bombardment mass-spectral analysis demonstrated that the hydroxy O atom comes from O2, but not from H2O, indicating that the alpha-hydroxylation should be a monooxygenase reaction.

Both induction and activation of the branched-chain 2-oxo acid dehydrogenase complex in primary-cultured rat hepatocytes by clofibrate

Clofibrate administration to rats caused both the activation and induction of the branched-chain 2-oxo acid dehydrogenase complex in the liver; the former phenomenon occurred within the first 6 h after clofibrate administration whereas the latter occurred after 12 h. Essentially the same results were obtained with primary cultures of rat hepatocytes in the presence of 0.5 mM clofibrate, though about three-fourths of the enzyme complex in control cells (without clofibrate addition) was inactivated during a culture for 44 h, with little reduction of the enzyme amount. This was also confirmed by immunotitration analysis with antibodies raised against the purified decarboxylase and transacylase components of the enzyme complex. On the other hand, the activity of dihydrolipoamide dehydrogenase (a constituent of the complex) was little affected by clofibrate administration. The half lives of the decarboxylase and transacylase components in the primary cultures were estimated to be in the range of 22-26 h, and were unchanged in the presence of clofibrate, when determined with the use of cycloheximide and by a pulse-chase experiment. On the contrary, the rates of synthesis of these two enzyme components had increased to about 1.9-fold after 32 h cultivation in the presence of clofibrate. Thus, the increase in the synthesis of both the components resulted in induction of the complex.

Purification and immunological characterization of a new form of gamma-glutamyltransferase of human semen

A new form of gamma-glutamyltransferase was purified from human seminal plasma. The purified enzyme was composed of two non-identical subunits with apparent molecular masses of 150 and 95 kDa on polyacrylamide gel electrophoresis (PAGE) in the presence of sodium dodecyl sulfate (SDS), and showed a molecular mass of 500 and 250 kDa on gel filtration in the absence and presence of 1% Triton X-100, respectively. This enzyme was different from human renal gamma-glutamyltransferase not only in apparent molecular masses, but also in amino acid compositions of both the subunits to each other. Experiments with the antisera raised against the purified enzyme revealed that the enzyme was different from the renal, hepatic and testicular enzymes in reactivity to the antibody though partially related to those enzymes. Ouchterlony double diffusion analysis indicated that both human seminal plasma and prostatic extract contained two types of gamma-glutamyltransferase, one is that we purified and the other the renal type. Hence, it is most likely that gamma-glutamyltransferase accounting for most of the enzyme activity in semen results from prostata followed by secretion to seminal plasma.

Regulation of hormonal induction of chick liver cytosol-specific phosphoenolpyruvate carboxykinase

Administration of glucagon, epinephrine, or dibutyryl cAMP to chicks induced cytosol-specific phosphoenolpyruvate carboxykinase in liver. In vitro translation assay with poly(A)+RNA indicated that this induction was due to the increase in phosphoenolpyruvate carboxykinase-coding mRNA synthesis which resulted from an increased level of hepatic cAMP. Either hydrocortisone or alpha-adrenergic agonist was ineffective for the induction by itself, but showed a significant effect when administered together with one of the inducing agents given above. In particular, hydrocortisone enhanced the synthesis of phosphoenolpyruvate carboxykinase-specific mRNA without changing the profile of the time courses of the induction and of hepatic cAMP level. Those observations suggest that the fundamental machinery required for induction of cytosol-specific phosphoenolpyruvate carboxykinase in liver is shared in common between rat and chick, and that the absence of appreciable induction of cytosol-specific hepatic phosphoenolpyruvate carboxykinase in starved chicks is due to neither lack nor impairment of the hormone-mediated induction mechanism, but is due to the difference in usage of the genetic information between the two animal species.

Regulation by induction of branched-chain 2-oxo acid dehydrogenase complex in clofibrate-fed rat liver

The activity of branched-chain 2-oxo acid dehydrogenase complex increased 3.0-fold in liver of rats fed on 0.1%(w/w) clofibrate. Immunotitration experiments with antibodies against the constituent enzymes of the complex revealed that this increase resulted mainly from the increased amounts of only two(a decarboxylase and a lipoate acyltransferase) of three components of the complex and that the other component(dihydrolipoamide dehydrogenase) remained unchanged in its content, irrespective of clofibrate administration. The increases of both enzyme components were associated with increases in their mRNA levels which were estimated by in vitro translation with poly(A)+ RNA.

Control of the activity of branched-chain alpha-keto acid dehydrogenase complex in primary cultured rat hepatocytes

When isolated rat hepatocytes were cultured in the medium containing 0.5 mM clofibrate (dissolved in ethanol) for 6 hours, the activity of branched-chain alpha-keto acid dehydrogenase (BCKADH) complex in the cells increased to more than two times that of control cells. Immunochemical determination with an anti-BCKADH IgG revealed that the activity increase occurred without increase in the enzyme amount. On the contrary, BCKADH activity in control cells (cultured in the presence 0.4% ethanol) decreased to two-third the initial activity at the end of 6-hour incubation whereas the activities of other enzymes tested were practically unaltered either in control or in clofibrate-treated cells. When the control cell extract was incubated with rat liver protein phosphatase, the BCKADH activity increased near to that of clofibrate-treated cells, but the same treatment of clofibrate-treated cell extract produced practically no increase in the activity. These observations indicate that clofibrate addition brought about the increase of BCKADH activity through activation-inactivation mechanism based on dephosphorylation-phosphorylation, and that this mechanism might function on liver BCKADH complex in vivo as a short term control of the activity in some conditions.

Cell surface heparan sulphate and adhesive property of sublines of rat ascites hepatoma AH7974

Two variants (74AD and 74FL) established from rat ascites hepatoma AH7974 were examined for the production of glycosaminoglycans in culture. There was no difference between the adhesive (74AD) and the floating (74FL) variants in quantity of glycosaminoglycans produced by their cultivation in minimum essential medium supplemented with 10% foetal calf serum. However, they were distinctly different in the distribution patterns of heparan sulphate. In 74FL, about 70% of total heparan sulphate was found in the culture medium in soluble form, whereas in 74AD, only 7% was found in the medium and the rest was in the cell-substratum complex. In a serum-free medium, 74AD cells grew without adhering to the substratum. After cultivation, more than 90% of total heparan sulphate was found in the cell-associated fractions and the rest in the substratum fractions. No heparan sulphate was detected in the culture medium. On the other hand, 74FL cells released heparan sulphate to the serum-free medium as much as to the serum-containing medium. The increase in amount of heparan sulphate in the culture medium of 74FL cells was supposed to be caused by failure of the cells to deposit heparan sulphate at the cell surface and not caused by increased production. Cell-substratum adhesion mechanisms involving cell surface heparan sulphate (heparan sulphate proteoglycan) and some serum intermediate(s) are discussed for 74AD cells.

Purification and characterization of human liver branched-chain alpha-keto acid dehydrogenase complex

Human liver BCKADH complex was purified. On SDS-polyacrylamide gel electrophoresis, the purified enzyme complex gave three major bands having molecular weights of 51,000, 46,000, and 36,000, and one minor band with a molecular weight of 55,000. The minor band corresponded in molecular weight to lipoamide oxidoreductase which was purified separately. The purified BCKADH represented only approximately 20% of the maximum activity when assayed without addition of exogenous lipoamide oxidoreductase, indicating that lipoamide oxidoreductase component was readily dissociable from the complex. The BCKADH effectively oxidized all of KIV, KIC, and KMV, yielding apparent Km values in the range of 14-17 microM for those alpha-keto acids. Vmax values obtained were 0.86, 0.61, and 0.51 mumole NADH produced/min/mg of protein for KIV, KIC, and KMV, respectively, in the presence of excess amount of lipoamide oxidoreductase. This ratio of Vmax values was practically identical to those of specific activities obtained with respective branched-chain alpha-keto acids at each purification step. The enzyme complex also oxidized pyruvate and alpha-ketoglutarate to a lesser extent. Kinetic experiments gave Km values of 0.98 and 2.9 mM for pyruvate and alpha-ketoglutarate, respectively, with Vmax of 0.43 and 0.08 mumole NADH produced/min/mg of protein. NAD and CoASH were absolutely required for the reaction. Km values for NAD and CoASH were estimated to be 47 and 25 microM, respectively.

Purification, resolution, and reconstitution of rat liver branched-chain alpha-keto acid dehydrogenase complex

Branched-chain alpha-keto acid dehydrogenase (BCKADH) was solubilized as an enzyme complex from rat liver mitochondria by sonic treatment. Dehydrogenase (E1) and dihydrolipoyltransacylase (E2) components of the complex were purified in an associated form and resolved into individual components in the presence of 1 M NaCl, while lipoamide dehydrogenase (E3) component was dissociated from the complex during purification. Analysis by gel electrophoresis in dodecyl sulfate revealed the E1 comprised two different subunits with apparent molecular weights of 36,000 and 45,500, presumably in an equal molar ratio, while E2 consisted of a single subunit with an apparent molecular weight of 51,000. The BCKADH complex was reconstituted by combining E1, E2, and E3, and the formation of the complex was confirmed by analysis by sucrose density gradient centrifugation. The reconstituted enzyme complex oxidized not only alpha-ketoisovalerate (KIV), alpha-ketoisocaproate (KIC), and alpha-keto-beta-methylvalerate (KMV), but also pyruvate and alpha-ketoglutarate. Apparent Km values were 10-12 microM for the branched-chain alpha-keto acids, 2.2 mM for pyruvate, and 2.5 mM for alpha-ketoglutarate.

Inhibition of glycine oxidation by pyruvate, alpha-ketoglutarate, and branched-chain alpha-keto acids in rat liver mitochondria: presence of interaction between the glycine cleavage system and alpha-keto acid dehydrogenase complexes

Pyruvate, alpha-ketoglutarate, and branched-chain alpha-keto acids which were transaminated products of valine, leucine, and isoleucine inhibited glycine decarboxylation by rat liver mitochondria. However, glycine synthesis (the reverse reaction of glycine decarboxylation) was stimulated by those alpha-keto acids with the concomitant decarboxylation of alpha-keto acid added in the absence of NADH. Both the decarboxylation and the synthesis of glycine by mitochondrial extract were affected similarly by alpha-ketoglutarate and branched-chain alpha-keto acids in the absence of pyridine nucleotide, but not by pyruvate. This failure of pyruvate to have an effect was due to the lack of pyruvate oxidation activity in the mitochondrial extract employed. It indicated that those alpha-keto acids exerted their effects by providing reducing equivalents to the glycine cleavage system, possibly through lipoamide dehydrogenase, a component shared by the glycine cleavage system and alpha-keto acid dehydrogenase complexes. On the decarboxylation of pyruvate, alpha-ketoglutarate, and branched-chain alpha-keto acids in intact mitochondria, those alpha-keto acids inhibited one another. In similar experiments with mitochondrial extract, decarboxylations of alpha-ketoglutarate and branched-chain alpha-keto acid were inhibited by branched-chain alpha-keto acid and alpha-ketoglutarate, respectively, but not by pyruvate. NADH was unlikely to account for the inhibition. We suggest that the lipoamide dehydrogenase component is an indistinguishable constituent among alpha-keto acid dehydrogenase complexes and the glycine cleavage system in mitochondria in nature, and that lipoamide dehydrogenase-mediated transfer of reducing equivalents might regulate alpha-keto acid oxidation as well as glycine oxidation.

Purification and characterization of cytosol-specific phosphoenolpyruvate carboxykinase from chicken liver

Phosphoenolpyruvate carboxykinase of chicken liver cytosol was purified to homogeneity by procedures including affinity chromatography with GTP as a ligand. The purified enzyme showed a molecular weight of 68,000 on gel electrophoresis in the presence of dodecyl sulfate. Comparative studies on this enzyme and its isozyme purified from chicken liver mitochondria were performed. As regards amino acid composition, the cytosolic enzyme was quite different from the mitochondrial enzyme, but was rather similar to rat liver cytosolic phosphoenolpyruvate carboxykinase. Specific activities of the cytosolic enzyme were 30-100% higher than those of the mitochondrial enzyme for oxaloacetate-CO2 exchange, oxaloacetate decarboxylation, and phosphoenolpyruvate carboxylation reactions, though the relative rates of the activities were similar, decreasing in the order given. Apparent Michaelis constants for oxaloacetate in the oxaloacetate decarboxylation reaction were 11.6 and 17.9 microM for the cytosolic and the mitochondrial enzyme, respectively, but the values for GTP, GDP, phosphoenolpyruvate, and CO2 in the oxaloacetate decarboxylation and phosphoenolpyruvate carboxylation reactions were 1.3-2.2 times higher for the cytosolic enzyme than for the mitochondrial enzyme. Thus, the fundamental catalytic properties of the chicken liver phosphoenolpyruvate carboxykinase isozymes were rather similar, despite the marked difference in amino acid compositions.

Studies on beta-lactam antibiotics VIII. Structure-activity relationships of 7 beta-[(Z)-2-carboxymethoxyimino-2-arylacetamido]-3-cephem- 4-carboxylic acids

The synthesis, antimicrobial activity and oral absorptivity of 7 beta-[(Z)-2-carboxymethoxyimino-2-arylacetamido]-3-cephem-4- carboxylic acids are described. The [(Z)-2-(2-amino-4-thiazolyl)-2-carboxymethoxyimino]acetyl group was selected as the most suitable 7-substituent from seven 7-acyl groups for our further investigation of orally active cephalosporins.

Fractionation and characterization of urinary heparan sulfate excreted by patients with Sanfilippo syndrome

Urinary heparan sulfates (HS) from two siblings with mucopolysaccharidosis (MPS) III-B were fractionated by chromatography with Dowex 1 and Sephadex G-50. Their Mr ranged from 1600 to 8000, and 95% of them were included in the region less than 5000. Fractions with lower Mr contained larger amounts of O-and N-sulfates. The chemical analysis and deaminative cleavage of HS suggested that an intact HS molecule was composed of some blocks rich in GlcNAc and GlcUA and other blocks rich in GlcNS, IdUA and O-sulfate. GlcNAc-UA-GlcNS-UA-GlcNAc-UA-GlcNAc was found to be a major oligosaccharide of HS with Mr less than 1800. Trisaccharides, GlcNAc-GlcUA-aMan and GlcNAc-IdUA-aMan, were released from the nonreducing end of HS-oligosaccharides by deaminative cleavage. They carried 0-3 moles of ester sulfate. GlcNAc-IdUA-aMan was more sulfated than the other. The release of significant amounts of nonsulfated trisaccharide conform to the enzyme defect in this disease. Urinary HS obtained from another patient with MPS III were examined by the same way. Although the patient was not examined enzymatically, the structure of urinary GAG suggested a defect of alpha-N-acetylglucosaminidase in the patient.

Formation of superoxide radicals after FeCl3 injection into rat isocortex

Subpial injection of aqueous solutions of iron salts into rat isocortex induces recurrent epileptiform discharges with focal brain edema, cavitary necrosis and gliosis. Since aqueous iron or heme compounds cause peroxidation of lipids, we studied the sequence of changes in the formation of free radicals, and superoxide radicals, in rat isocortex injected with 5 microliter of 100 mM FeCl3. Electron spin resonance measurements of whole rat brain showed a transient increase in heme-bound Fe3+. Superoxide radicals were increased in a cylinder of tissue obtained at the injection site 5 min and 15 min after completion of the injection. This study shows that iron salts injected into rat isocortex cause transient formation of free radicals. We suggest that decompartmentalization of iron compounds may be of importance in trauma-related brain injury responses.

Studies on beta-lactam antibiotics. VII. Effect on antibacterial activity of the oxime O-substituents with various functional groups in the 7 beta-[(Z)-2-(2-amino-4-thiazolyl)-2-oxyiminoacetamido]cephalosporins

The synthesis and in vitro activity of the 7-[O-substituted oxyiminoacetamido]cephalosporins (I) without substitution at 3-position of a cephem nucleus are described. Effect of changing the oxime O-substituents (R1) with various functional groups in the 7-acyl residue on antibacterial activity was examined. Against Gram-positive bacteria, cephems with hydrophilic functions in the R1 moiety such as hydroxyethyl, aminoethyl and carboxymethyl groups showed decrease of the activity, while cephems with lipophilic functions such as cyanomethyl, methylthiomethyl and halogenoethyl groups exhibited increase of the activity. However, influence of the substituents (R1) on activity against Gram-negative bacteria was observed to be relatively independent of the nature of their functional groups.

Studies on beta-lactam antibiotics. II. Synthesis and structure-activity relationships of alpha-hydroxyiminoarylacetyl cephalosporins

The synthesis and antibacterial activity in vitro of the 2-aryl-2-hydroxyiminoacetyl cephalosporins (2) are described. Within this cephalosporin series, analogs (9f approximately 13f) with 2-hydroxyimino-2-(3-hydroxyphenyl)acetyl group at the 7-position of a cephem nucleus were found to have the highest antibacterial activity against a wide-range of microorganisms, including beta-lactamase-producing bacteria. Structure-activity relationships of 2 are discussed.

Defective glycine cleavage system in nonketotic hyperglycinemia. Occurrence of a less active glycine decarboxylase and an abnormal aminomethyl carrier protein

The activities of then glycine cleavage system in the liver and brain of patient with nonketotic hyperglycinemia was extremely low as compared with those of control human liver and brain. The activities of glycine decarboxylase (P-protein) and the aminomethyl carrier protein (H-protein), two of the four protein components of the glycine cleavage system, were considerably reduced in both the liver and brain; the extent of reduction was greater in the H-protein. The activity of the T-protein was normal. Purified H-protein from the patient did not react with lipoamide dehydrogenase, and titration of thiol groups with [2,3-14C]N-ethylmaleimide suggested that this H-protein is devoid of lipoic acid. This structural abnormality in the H-protein is considered to constitute the primary molecular lesion in this patient with non-ketotic hyperglycinemia. Immunochemical studies using an antibody specific for P-protein showed that the patient was due to reduction of the catalytic activity of the protein rather than a decrease in the actual amount of the P-protein. Partial inactivation of P-protein could result secondarily from impaired metabolism of glycine resulting from deficiency in the activity of H-protein. However, the H-protein from the patient could stimulate the P-protein catalyzed exchange of the carboxyl carbon of glycine with 14CO2, although the specific activity of the purified H-protein from the patient was only 4% of that of control human H-protein. The content of H-protein in the liver of the patient was approximately 35% of that of control human liver.

Purification and properties of glycine decarboxylase, a component of the glycine cleavage system, from rat liver mitochondria and immunochemical comparison of this enzyme from various sources

Glycine decarboxylase, tentatively called P-protein as a constituent of the glycine cleavage system, was purified to near homogeneity from rat liver mitochondria. The purified P-protein was a homodimer with a molecular weight of about 210,000, consisting of identical subunits with a molecular weight of 105,000. In the exchange reaction of the carboxyl carbon of glycine wih CO2 catalyzed by the purified P-protein in the presence of H-protein, the pH optimum was 6.7, Km for glycine was 6.6 mM, and Km for H-protein was 7.4 microM. A specific rabbit antibody against the purified rat liver P-protein was prepared. Ouchterlony double diffusion analysis and immunoinhibition experiments using this antibody revealed immunological cross-reactivity among the P-proteins from various species of animals such as carp, frog, snake, chicken, bovine, and human, suggesting a quite conservative evolution of the glycine cleavage system.

On the nature of three forms of phosphoenolpyruvate carboxykinase occurring in the cytosol of chicken liver

Chicken liver mitochondria contained two forms of phosphoenolpyruvate (PEP) carboxykinase (designated as Mt-I and Mt-II) and the chicken liver cytosol fraction contained three forms of PEP carboxykinase (designated as Sol-I, Sol-II, and Sol-III). Mt-I and Mt-II were purified to homogeneity. They both had a molecular weight of 72,000 as judged by the sodium dodecyl-sulfate-polyacrylamide gel electrophoresis method, whereas an apparent molecular weight of 42,000 was obtained for both enzymes when estimated by Sephadex G-100 gel filtration. Studies with a rabbit antibody against the purified Mt-I revealed that Mt-I, Mt-II, Sol-I, and Sol-II are immunochemically identical, whereas Sol-III is immunochemically different from any of the other proteins. Genetic analogy between Mt-I and Mt-II was also suggested by gel electrophoretic analysis of their peptide maps. The content of Sol-III in the adult chicken liver was very small, whereas the livers of chick embryo and very young chick contained a considerable amount of Sol-III. The level of Sol-III in the adult chicken, however, could be significantly increased by the administration of hydrocortisone or isoproterenol. Apparently Sol-III is a cytosol-specific PEP carboxykinase which is similar to the cytosolic PEP carboxykinases of various mammals. Sol-III showed a molecular weight of about 60,000 as estimated by gel filtration. Studies with combined use of the antibody and [3H]leucine revealed that some portion of PEP carboxykinase (Sol-I plus Sol-II) appearing in the liver cytosol corresponds to a precursor in transit to the mitochondria, although major portions of Sol-I and Sol-II appear to be accounted for by release of the mitochondrial enzymes.