3'-phosphoadenosine 5'-phosphosulphate metabolism in mammalian tissues

Internalization and trafficking of CSPG-bound recombinant VAR2CSA lectins in cancer cells

Proteoglycans are proteins that are modified with glycosaminoglycan chains. Chondroitin sulfate proteoglycans (CSPGs) are currently being exploited as targets for drug-delivery in various cancer indications, however basic knowledge on how CSPGs are internalized in tumor cells is lacking. In this study we took advantage of a recombinant CSPG-binding lectin VAR2CSA (rVAR2) to track internalization and cell fate of CSPGs in tumor cells. We found that rVAR2 is internalized into cancer cells via multiple internalization mechanisms after initial docking on cell surface CSPGs. Regardless of the internalization pathway used, CSPG-bound rVAR2 was trafficked to the early endosomes in an energy-dependent manner but not further transported to the lysosomal compartment. Instead, internalized CSPG-bound rVAR2 proteins were secreted with exosomes to the extracellular environment in a strictly chondroitin sulfate-dependent manner. In summary, our work describes the cell fate of rVAR2 proteins in tumor cells after initial binding to CSPGs, which can be further used to inform development of rVAR2-drug conjugates and other therapeutics targeting CSPGs.

Skeletal Dysplasias Caused by Sulfation Defects

Proteoglycans (PGs) are macromolecules present on the cell surface and in the extracellular matrix that confer specific mechanical, biochemical, and physical properties to tissues. Sulfate groups present on glycosaminoglycans, linear polysaccharide chains attached to PG core proteins, are fundamental for correct PG functions. Indeed, through the negative charge of sulfate groups, PGs interact with extracellular matrix molecules and bind growth factors regulating tissue structure and cell behavior. The maintenance of correct sulfate metabolism is important in tissue development and function, particularly in cartilage where PGs are fundamental and abundant components of the extracellular matrix. In chondrocytes, the main sulfate source is the extracellular space, then sulfate is taken up and activated in the cytosol to the universal sulfate donor to be used in sulfotransferase reactions. Alteration in each step of sulfate metabolism can affect macromolecular sulfation, leading to the onset of diseases that affect mainly cartilage and bone. This review presents a panoramic view of skeletal dysplasias caused by mutations in genes encoding for transporters or enzymes involved in macromolecular sulfation. Future research in this field will contribute to the understanding of the disease pathogenesis, allowing the development of targeted therapies aimed at alleviating, preventing, or modifying the disease progression.

Preparation of Tyrosylprotein Sulfotransferases for In Vitro One-Pot Enzymatic Synthesis of Sulfated Proteins/Peptides

Protein tyrosine sulfation (PTS), catalyzed by membrane-anchored tyrosylprotein sulfotransferase (TPST), is one of the most common post-translational modifications of secretory and transmembrane proteins. PTS, a key modulator of extracellular protein-protein interactions, accounts for various important biological activities, namely, virus entry, inflammation, coagulation, and sterility. The preparation and characterization of TPST is fundamental for understanding the synthesis of tyrosine-sulfated proteins and for studying PTS in biology. A sulfated protein was prepared using a TPST-coupled protein sulfation system that involves the generation of the active sulfate 3'-phosphoadenosine-5'-phosphosulfate (PAPS) through either PAPS synthetase (PAPSS) or phenol sulfotransferase. The preparation of sulfated proteins was confirmed through radiometric or immunochemical assays. In this study, enzymatically active Drosophila melanogaster TPST (DmTPST) and human TPSTs (hTPST1 and hTPST2) were expressed in Escherichia coli BL21(DE3) host cells and purified to homogeneity in high yield. Our results revealed that recombinant DmTPST was particularly useful considering its catalytic efficiency and ease of preparation in large quantities. This study provides tools for high-efficiency, one-step synthesis of sulfated proteins and peptides that are useful for further deciphering the mechanisms, functions, and future applications of PTS.

Sulfation of Glycosaminoglycans and Its Implications in Human Health and Disorders

Sulfation is a dynamic and complex posttranslational modification process. It can occur at various positions within the glycosaminoglycan (GAG) backbone and modulates extracellular signals such as cell-cell and cell-matrix interactions; different sulfation patterns have been identified for the same organs and cells during their development. Because of their high specificity in relation to function, GAG sulfation patterns are referred to as the sulfation code. This review explores the role of GAG sulfation in different biological processes at the cell, tissue, and organism levels. We address the connection between the sulfation patterns of GAGs and several physiological processes and discuss the misregulation of GAG sulfation and its involvement in several genetic and metabolic disorders. Finally, we present the therapeutic potential of GAGs and their synthetic mimics in the biomedical field.

A jumbo phage infecting the phytopathogen Ralstonia solanacearum defines a new lineage of the Myoviridae family

phiRSL1 is a jumbo myovirus stably and lytically infecting the phytopathogenic bacterium Ralstonia solanacearum. In this study, we investigate the infection cycle of varphiRSL1 and provide a genomic, proteomic and transcriptomic view of this phage. Its 231-kbp genome sequence showed many genes lacking detectable homologs in the current databases and was vastly different from previously studied phage genomes. In addition to these orphan proteins, varphiRSL1 was found to encode several enzymes that are unique among known viruses. These include enzymes for the salvage pathway of NAD(+) and for the biosynthetic pathways of lipid, carbohydrate and homospermidine. A chitinase-like protein was found to be a potential lysis enzyme. Our proteomics analysis suggests that varphiRSL1 virions contain at least 25 distinct proteins. We identified six of them including a tail sheath protein and a topoisomerase IB by N-terminal sequencing. Based on a DNA microarray analysis, we identified two transcription patterns.

Steroid sulfatase and sulfuryl transferase activities in human brain tumors

Neuroactive steroids (dehydroepiandrosterone, pregnenolone) and their sulfates act as modulators of glutamate and gamma-aminobutyrate type A receptors in the brain The physiological ratio of these neuromodulators is maintained by two enzymes present in the brain, namely, steroid sulfatase (STS) and steroid sulfuryl transferase (SULT). Following previous determination of their activities in monkey brains, their activities were evaluated in human brain tumors. Radioimmunoassay and GC-MS were used for determination of products. Both enzyme activities were measured in the 55 most frequent human brain tumors (glioblastomas, pituitary adenomas, meningiomas, astrocytomas). Significant differences were found in STS activity among investigated types of tumors except the pair of pituitary adenomas-glioblastomas, while significant differences were found in SULT activity among investigated types of tumors. Spontaneous tendency to form clusters was revealed when both enzyme activities were taken as coordinates. Clustering indicated an individual metabolic behavior of glioblastomas and 72.7% of pituitary adenomas. Astrocytomas, meningiomas and remaining 27.3% pituitary adenomas showed similarities in both enzymes' activities. Differences in STS and SULT activity did not depend on the sex or age of subjects.

The essentiality of sulfur is closely related to nitrogen metabolism: a clue to hyperhomocysteinaemia

N and S metabolisms are closely interwoven throughout both the plant and animal kingdoms. The essentiality of S relates to its participation in the structure of S-containing amino acids (SAA), to its inclusion in many sulfonated molecules, and to a myriad of metabolic and catalytic reactions of vital importance. Methionine (Met) is the indispensable SAA supplied by food proteins and its plasma homeostasis is achieved via a number of highly efficient regulatory mechanisms. In all conditions characterised by a negative body protein balance such as in dietary restriction or cytokine-induced hypercatabolic losses, N and S endogenous pools manifest parallel tissue depletion rates. Adaptive conservation of N and S body stores is reached by a functional restraint of the trans-sulfuration cascade, through the depression of cystathionine β-synthase activity. As a result, upstream accumulation of homocysteine favours its re-methylation conversion to Met which helps maintain metabolic pathways of survival value. In addition to the measurement of vitamin indices, that of plasma transthyretin, a sensitive marker of protein nutritional status, is proposed to identify the fluctuations of the total body N component accountable for the alterations of homocysteine concentrations in body fluids.

Human chorionic gonadotropin-dependent up-regulation of genes responsible for estrogen sulfoconjugation and export in granulosa cells of luteinizing preovulatory follicles

Estrogen sulfotransferase (EST) is responsible for the sulfoconjugation of estrogens, thereby changing their physical properties and preventing their action via the estrogen receptors. These sulfoconjugated steroids no longer diffuse freely across the lipid bilayer; instead, they are exported by members of the ATP-binding cassette family, such as ABCC1. The objective of this study was to investigate the regulation of EST and ABCC1 during human chorionic gonadotropin (hCG)-induced ovulation/luteinization. The transcripts for EST and ABCC1 were cloned by RT-PCR, and the regulation of their mRNAs was studied in preovulatory follicles obtained during estrus at 0, 12, 24, 30, 33, 36, and 39 h after hCG. Results obtained from RT-PCR/Southern blot analyses showed significant changes in steady-state levels of both EST and ABCC1 mRNA after hCG treatment (P < 0.05). In granulosa cells, a significant increase in EST transcript was observed 30-39 h after hCG. Similarly, ABCC1 transcript levels were induced in granulosa cells 12-39 h after hCG. In contrast, no significant changes in either EST or ABCC1 were detected in theca interna samples after hCG. The increase in EST and ABCC1 transcripts observed in granulosa cells was reflected in preparations of intact follicle walls, suggesting that the granulosa cell layer contributes the majority of EST and ABCC1 expression in preovulatory follicles. The present study demonstrates that follicular luteinization is accompanied not only by a decrease in 17 beta-estradiol biosynthesis but also by an increase in expression of genes responsible for estrogen inactivation and elimination from granulosa cells, such as EST and ABCC1, respectively.

Steroid sulfatase and sulfuryl transferase activity in monkey brain tissue

Dehydroepiandrosterone and its sulfated form are commonly known as modulators of gamma-aminobutyrate A and N-methyl-D-aspartate receptors. In spite of poor permeability of the blood-brain barrier for sulfated steroids, high concentrations of dehydroepiandrosterone and also its sulfate have been found in brain tissue. Physiological concentrations of these neuromodulators are maintained by two enzymes present in the blood and many peripheral tissues, including the brain, namely, steroid sulfatase and neurosteroid sulfuryl transferase (NSST). This prompted us to investigate activities of these enzymes in primate brain tissue. Rather low neurosteroid sulfuryl transferase activity was detectable in in vitro incubations of cytosol fractions from male and female Macaca mulatta brains, dissected to cerebral cortex, subcortex, and cerebellum. In male monkeys, the highest activity was found in the cerebellum followed by cortex and subcortex. On the other hand, in female monkeys, the highest activity was determined in the cortex followed by subcortex and cerebellum. Steroid sulfatase activity was determined in in vitro microsomal samples from each of the above-mentioned brain regions. Specific activities in female cerebral regions declined in the order: cerebellum, cortex, and subcortex. In male monkeys, no significant difference among the studied regions was observed. Using dehydroepiandrosterone sulfate as a substrate, the apparent kinetic characteristics of steroid sulfatase were determined as follows: K(M) 36.10 +/- 8.33 microM, V(max) 8.38 +/- 1.68 nmol/h/mg protein. These results will serve as a basis for further studies concerning the pathophysiology of human brain tumors.

Pharmacogenetics of human 3'-phosphoadenosine 5'-phosphosulfate synthetase 1 (PAPSS1): gene resequencing, sequence variation, and functional genomics

3'-Phosphoadenosine 5'-phosphosulfate (PAPS) is the high-energy "sulfate donor" for reactions catalyzed by sulfotransferase (SULT) enzymes. The strict requirement of SULTs for PAPS suggests that PAPS synthesis might influence the rate of sulfate conjugation. In humans, PAPS is synthesized from ATP and SO(4)(2-) by two isoforms of PAPS synthetase (PAPSS): PAPSS1 and PAPSS2. As a step toward pharmacogenetic studies, we have resequenced the entire coding sequence of the human PAPSS1 gene, including exon-intron splice junctions, using DNA samples from 60 Caucasian-American and 58 African-American subjects. Twenty-one genetic polymorphisms were observed-1 insertion-deletion event and 20 single nucleotide polymorphisms (SNPs)-including two non-synonymous coding SNPs (cSNPs) that altered the following amino acids: Arg333Cys and Glu531Gln. Twelve pairs of these polymorphisms were tightly linked, and a total of twelve unequivocal haplotypes could be identified-two that were common to both ethnic groups and ten that were ethnic-specific. The Arg333Cys polymorphism, with an allele frequency of 2.5%, was observed only in DNA samples from Caucasian subjects. The Glu531Gln polymorphism was rare, with only a single copy of that allele in a DNA sample from an African-American subject. Transient expression in mammalian cells showed that neither of the non-synonymous cSNPs resulted in a change in the basal level of enzyme activity measured under optimal assay conditions. However, the Glu531Gln polymorphism altered the substrate kinetic properties of the enzyme. The Gln531 variant allozyme had a 5-fold higher K(m) value for SO(4)(2-) than did the wild-type allozyme and displayed monophasic kinetics for Na(2)SO(4). The wild-type allozyme (Glu531) showed biphasic kinetics for that substrate. These observations represent a step toward testing the hypothesis that genetic variation in PAPS synthesis catalyzed by PAPSS1 might alter in vivo sulfate conjugation.

Sulfonation and molecular action

The sulfonation of endogenous molecules is a pervasive biological phenomenon that is not always easily understood, and although it is increasingly recognized as a function of fundamental importance, there remain areas in which significant cognizance is still lacking or at most minimal. This is particularly true in the field of endocrinology, in which the sulfoconjugation of hormones is a widespread occurrence that is only partially, if at all, appreciated. In the realm of steroid/sterol sulfoconjugation, the discovery of a novel gene that utilizes an alternative exon 1 to encode for two sulfotransferase isoforms, one of which sulfonates cholesterol and the other pregnenolone, has been an important advance. This is significant because cholesterol sulfate plays a crucial role in physiological systems such as keratinocyte differentiation and development of the skin barrier, and pregnenolone sulfate is now acknowledged as an important neurosteroid. The sulfonation of thyroglobulin and thyroid hormones has been extensively investigated and, although this transformation is better understood, there remain areas of incomplete comprehension. The sulfonation of catecholamines is a prevalent modification that has been extensively studied but, unfortunately, remains poorly understood. The sulfonation of pituitary glycoprotein hormones, especially LH and TSH, does not affect binding to their cognate receptors; however, sulfonation does play an important role in their plasma clearance, which indirectly has a significant effect on biological activity. On the other hand, the sulfonation of distinct neuroendocrine peptides does have a profound influence on receptor binding and, thus, a direct effect on biological activity. The sulfonation of specific extracellular structures plays an essential role in the binding and signaling of a large family of extracellular growth factors. In summary, sulfonation is a ubiquitous posttranslational modification of hormones and extracellular components that can lead to dramatic structural changes in affected molecules, the biological significance of which is now beginning to be appreciated.

Human 3'-phosphoadenosine 5'-phosphosulfate synthetase 2 (PAPSS2) pharmacogenetics: gene resequencing, genetic polymorphisms and functional characterization of variant allozymes

3'-Phosphoadenosine 5'-phosphosulfate (PAPS) is the sulfate donor cosubstrate for all sulfotransferase (SULT) enzymes. SULTs catalyze the sulfate conjugation of many endogenous and exogenous compounds, including drugs and other xenobiotics. In humans, PAPS is synthesized from adenosine 5'-triphosphate (ATP) and inorganic sulfate (SO2-4) by two isoforms, PAPSS1 and PAPSS2. Rare mutations that inactivate PAPSS2 are associated with human spondyloepimetaphyseal dysplasia and murine brachymorphism. To determine whether more common genetic polymorphisms that do not completely inactivate the enzyme might be one factor responsible for individual differences in sulfate conjugation, we previously cloned the human PAPSS2 gene. In the present studies, we 'resequenced' all twelve PAPSS2 exons and splice junctions, as well as approximately 500 bp of the 5'-flanking region, using 90 Polymorphism Discovery Resource (PDR) DNA samples from the Coriell Cell Repository. Twenty-two single nucleotide polymorphisms (SNPs) were observed, including four nonsynonymous coding region SNPs (cSNPs) that altered the following amino acids: Glu10Lys, Met281Leu,Val291Met and Arg432Lys. We also observed four insertions/deletions, including one sample that was homozygous for an 81-bp deletion in the 5'-flanking region 286 bp upstream from the site of transcription initiation. Transient expression studies showed that two of the nonsynonymous cSNPS, those that resulted in Glu10Lys and Val291Met alterations in encoded amino acids, showed significant decreases in levels of PAPSS activity. In the case of Glu10Lys, decreased activity was paralleled by a decrease in immunoreactive protein, while the Val291Met allozyme displayed a significant decrease in affinity for both ATP and Na2SO4 when compared to 'wild-type' enzyme, but without a significant alteration in level of immunoreactive protein. It will now be possible to test the hypothesis that these common, functionally significant PAPSS2 genetic polymorphisms might contribute to variations in sulfate conjugation in vivo.

Human 3'-phosphoadenosine 5'-phosphosulfate synthetase 1 (PAPSS1) and PAPSS2: gene cloning, characterization and chromosomal localization

Sulfae conjugation is an important pathway in the metabolism of a large number of exogenous and endogenous compounds. These reactions are catalyzed by sulfotransferase (SULT) enzymes that utilize 3'-phosphoadenosine 5'-phosphosulfate (PAPS) as a sulfate donor. PAPS is synthesized from ATP and inorganic sulfate by PAPS synthetase (PAPSS). Two separate PAPSS cDNAs, PAPSS1 and PAPSS2, have been identified in human tissues. We have cloned and characterized the genes for human PAPSS1 and PAPSS2 to make it possible to study the pharmacogenomics of these enzymes. Both genes consisted of 12 exons with virtually identical exon-intron splice junction locations. All splice junctions conformed to the "GT-AG" rule. The total length of PAPSS1 was approximately 108 kb, while that of PAPSS2 was greater than 37 kb. The 5'-flanking region of PAPSS1 did not include a TATA box sequence near the site of transcription initiation, but PAPSS2 had a TATA motif located 21 bp upstream from the site of transcription initiation. Northern blot analysis showed that the major PAPSS1 and PAPSS2 transcripts were approximately 2.7 and 4.2 kb in length, respectively. PAPSS1 mapped to human chromosome band 4q24 while PAPSS2 mapped to 10q22-23 by fluorescence in situ hybridization analysis. Cloning and structural characterization of PAPSS1 and PAPSS2 will make it possible to perform molecular genetic and pharmacogenomic studies of these important enzymes in humans.

Nuclear localization of PAPS synthetase 1: a sulfate activation pathway in the nucleus of eukaryotic cells

Sulfation is a major modification of many molecules in eukaryotes that is dependent on the enzymatic synthesis of an activated sulfate donor, 3'-phosphoadenosine 5'-phosphosulfate (PAPS). While sulfate activation has long been assumed to occur in the cytosol, we show in this study that human PAPS synthetase 1 (PAPSS1), a bifunctional ATP sulfurylase/adenosine 5'-phosphosulfate (APS) kinase enzyme sufficient for PAPS synthesis, accumulates in the nucleus of mammalian cells. Nuclear targeting of the enzyme is mediated by its APS kinase domain and requires a catalytically dispensable 21 amino acid sequence at the amino terminus. Human PAPSS1 and Drosophila melanogaster PAPSS localize to the nucleus in yeast and relieve the methionine auxotrophy of ATP sulfurylase- or APS kinase-deficient strains, suggesting that PAPSS1 is fully functional in vivo when targeted to the nucleus. A second PAPS synthetase gene, designated PAPSS2, has recently been described, mutations of which are responsible for abnormal skeletal development in human spondyloepimetaphyseal dysplasia and murine brachymorphism. We found that PAPSS2, which localizes to the cytoplasm when ectopically expressed in mammalian cells, is relocated to the nucleus when coexpressed with PAPSS1. Taken together, these results indicate that a sulfation pathway might exist in the nucleus of eukaryotic cells. -Besset, S., Vincourt, J.-B., Amalric, F., Girard, J.-P. Nuclear localization of PAPS synthetase 1: a sulfate activation pathway in the nucleus of eukaryotic cells.

Molecular cloning, expression, and characterization of human bifunctional 3'-phosphoadenosine 5'-phosphosulfate synthase and its functional domains

The universal sulfonate donor, 3'-phosphoadenosine 5'-phosphosulfate (PAPS), is synthesized by the concerted action of ATP sulfurylase and adenosine 5'-phosphosulfate (APS) kinase, which in animals are fused into a bifunctional protein. The cDNA for human PAPS synthase (hPAPSS) along with polymerase chain reaction products corresponding to several NH2- and COOH-terminal fragments were cloned and expressed in COS-1 cells. A 1-268-amino acid fragment expressed APS kinase activity, whereas a 220-623 fragment evinced ATP sulfurylase activity. The 1-268 fragment and full-length hPAPSS (1-623) exhibited hyperbolic responses against APS substrate with equivalent Km values (0.6 and 0.4 microM, respectively). The 1-268 fragment demonstrated Michaelis-Menten kinetics against ATP as substrate (Km 0.26 mM); however, full-length hPAPSS exhibited a sigmoidal response (apparent Km 1.5 mM) suggesting cooperative binding. Catalytic efficiency (Vmax/Km) of the 1-268 fragment was 64-fold higher than full-length hPAPSS for ATP. The kinetic data suggest that the COOH-terminal domain of hPAPSS exerts a regulatory role over APS kinase activity located in the NH2-terminal domain of this bifunctional protein. In addition, the 1-268 fragment and full-length hPAPSS were overexpressed in Escherichia coli and column purified. Purified full-length hPAPSS, in contrast to the COS-1 cell-expressed cDNA construct, exhibited a hyperbolic response curve against ATP suggesting that hPAPSS is perhaps modified in vivo.

Kinetic mechanism of adenosine 5'-phosphosulphate kinase from rat chondrosarcoma

Biosynthesis of the activated sulphate donor adenosine 3'-phosphate 5'-phosphosulphate (PAPS) involves the sequential action of two enzyme activities. ATP-sulphurylase catalyses the formation of APS (adenosine 5'-phosphosulphate) from ATP and free sulphate, and APS is then phosphorylated by APS kinase to produce PAPS. Initial-velocity patterns for rat chondrosarcoma APS kinase indicate a single-displacement formal mechanism with KmAPS 76 nM and KmATP = 24 microM. Inhibition studies using analogues of substrates and products were carried out to determine the reaction mechanism. An analogue of PAPS, adenosine 3'-phosphate 5'-[beta-methylene]phosphosulphate, exhibited competitive inhibition with APS and non-competitive inhibition with ATP. An analogue of APS, adenosine 5'-[beta-methylene]phosphosulphate was also competitive with APS and non-competitive with ATP. Adenosine 5'-[beta gamma-imido]triphosphate showed competitive inhibition with respect to ATP and produced mixed-type inhibition, with a pronounced intercept effect and a small slope effect, with respect to APS. These results are in accord with the formulation of the predominant pathway as a steady-state ordered mechanism with APS as the leading substrate and PAPS as the final product released.

Intermediate channeling between ATP sulfurylase and adenosine 5'-phosphosulfate kinase from rat chondrosarcoma

Biosynthesis of the activated sulfate donor PAPS (3'-phosphoadenosine 5'-phosphosulfate) involves the sequential action of two enzyme activities. ATP sulfurylase catalyzes the formation of APS (adenosine 5'-phosphosulfate) from ATP and free sulfate, and APS is then phosphorylated by APS kinase to produce PAPS. Using rat chondrosarcoma ATP sulfurylase and APS kinase, a newly developed assay system, which permits measuring the accumulation of both APS and PAPS in the presence of both enzyme activities, produces a PAPS/APS ratio corresponding to a "channeling efficiency" of 96%. The velocity of the APS kinase reaction measured in the overall system with endogenously synthesized APS is 8-fold greater than that of the isolated kinase reaction using exogenous APS. Most conclusively, isotope dilution and enrichment experiments show that the APS intermediate does not equilibrate with APS in the bulk medium but remains largely bound in the rat enzyme system. In contrast, control experiments with a nonchanneled system containing a mixture of the sulfurylase and kinase isolated from Penicillium chrysogenum give the results expected for a nonchanneled pathway. These data indicate that APS is channeled between the active sites of ATP sulfurylase and APS kinase during the production of PAPS in rat chondrosarcoma.

3'-Phosphoadenosine 5'-phosphosulfate biosynthesis and the sulfation of cholecystokinin by the tyrosylprotein-sulfotransferase in rat brain tissue

This article resumes the work we have accomplished in the past few years. Cholecystokinin sulfation is an important post-translational modification necessary for the biological activity of this peptide hormone. The tyrosyl protein sulfotransferase (TPST) activity from rat cerebral cortex was characterized. TPST activity is most probably responsible for the endogenous sulfation of CCK. TPST reaction kinetic properties were studied using radiolabeled 3'-phosphoadenosine 5'-phosphosulfate (PAPS) and the non-sulfated peptide acceptor terbutyloxycarbonyl-cholecystokinin octapeptide (BocCCK-8(ns)) as substrates, and brain microsomes as the enzyme source. The BocCCK-8 sulfating reaction data is consistent with the idea that TPST forward reaction follows an ordered Bi Bi mechanism. PAPS biosynthesis and availability was studied in slices from rat cerebral cortex incubated in the presence of [35S]sulfate. There is a rapid and dynamic turnover of the steady-state level of PAPS in brain cells which is decreased by depolarizing agents such as potassium, veratridine and glutamate. Furthermore, the presence of a membrane-bound PAPS biosynthesis inhibitor was observed. These results are discussed in view of the biological importance that the cell sulfating pathways might play in nerve cell activity.

The differential effects of hepatotoxicants on the sulfation pathway in rats

This study characterized the effects of liver damage produced by a variety of hepatotoxicants on several components of the sulfation pathway in rats. Specifically, the concentration of cosubstrate, adenosine 3'-phosphate 5'-phosphosulfate (PAPS), and the hepatic capacity for PAPS synthesis were measured in livers of rats treated with carbon tetrachloride (CCl4), 1,1-dichloroethylene (DCE), alpha-naphthylisothiocyanate (ANIT), aflatoxin B1 (ATX), allyl alcohol (AA), bromobenzene (BB), cadmium chloride (Cd), or thioacetamide (TA). Liver damage was assessed by measuring serum sorbitol dehydrogenase (SDH) and alanine aminotransferase (ALT) activities as well as by histopathological examination. Hepatic PAPS concentration was generally decreased as a result of treatment with hepatotoxicants (35-80% of control), although BB, AA, and ANIT were without effect. Maximal hepatic capacity for PAPS synthesis, determined as the activities of PAPS synthetic enzymes, ATP sulfurylase, and APS kinase, was selectively decreased by the hepatotoxicants. ATP sulfurylase activity was decreased by Cd and TA (55 and 62% of control, respectively), whereas APS kinase activity was decreased by Cd, TA, BB, and DCE (60-77% of control, respectively). In addition, phenol sulfotransferase (PST) activity was measured toward 1- and 2-naphthol in order to determine whether apparent changes in PST activity in damaged livers are substrate-dependent. Treatment with hepatotoxicants generally decreased 1-naphthol-directed PST activity but not PST activity directed toward 2-naphthol. In conclusion, (1) not all xenobiotic-induced liver injury results in decreased hepatic PAPS concentration, (2) some hepatotoxicants decrease PAPS concentration by a mechanism other than decreased cosubstrate synthesis, and (3) the effect of hepatotoxicants on PST activity is dependent upon the choice of substrate used in the enzymatic assay.

Biosynthesis of PAPS in vitro by human liver. Measurement by two independent assay procedures

The biosynthesis of 3'-phosphoadenosine-5'-phosphosulphate (PAPS) by extracts of human liver from inorganic sulphate and APS was assayed by transferring the "active sulphate" to two different acceptors, namely N-acetyldopamine (NADA) and 4-methylumbelliferone (4-MU). NADA-sulphate was quantified by an HPLC-ECD method while the decrease in 4-MU was monitored continuously by a fluorimetric procedure. The optimum pH was 8.0 for both the PAPS generation and APS-kinase reaction. The apparent Km value for APS determined by the fluorimetric and HPLC-ECD procedures was 17.6 and 16.8 microM, respectively. PAPS-generation measured in 13 samples of human liver showed excellent correlation between the two assay procedures, with correlation coefficients (r) of 0.96 and 0.95 for PAPS generation from inorganic sulphate and APS, respectively. The fluorimetric assay was preferred as it is simple, equally sensitive and more reproducible. There was also a good correlation between the APS-kinase reaction and the two-step PAPS-generation from inorganic sulphate, with r = 0.97 and 0.91, as determined by the fluorimetric and HPLC-ECD procedures. The rate of PAPS generation from inorganic sulphate was only marginally less than that from APS in each of the 13 human liver samples, suggesting that the coupling of ATP-sulphurylase to APS-kinase facilitates "sulphate activation" and releases it from the constraints imposed by the unfavourable ATP sulphurylase reaction.

A low Km nucleoside 3'(2'),5-bisphosphate 3'(2')-phosphohydrolase from rat liver

In the course of an investigation on the occurrence in rat liver of a specific hydrolytic activity on adenosine 2',5'-bisphosphate, a nucleoside 3'(2'),5'-bisphosphate 3'(2')-phosphohydrolase was purified following standard procedures. The enzyme hydrolyzes the phosphate group joined to the 3' or the 2' position of the following nucleotides (relative velocities indicated in brackets): PAdoP (100), PCydP (95), PGuoP (80), PAdo2'P (40), PdAdoP (4), SPAdoP (18). Other nucleotides were not substrates of the reaction: NADP+, PAdoPP, PPGuoP, AdoP, PAdo, GuoP, PGuo, ADP, ATP, cAMP, adenosine(3')phospho(5')adenosine. The Km values determined for PAdoP and PAdo2'P were 10 and 7 microM, respectively. Two isoforms were separated by chromatography on a Mono Q column. Both isoforms were kinetically indistinguishable, presenting a pI value of 5.35, a molecular mass of 38 kDa, pH optimum of 8.0, and strictly required Mg2+ or Mn2+. An enzymatic activity similar to the one described here has already been reported in guinea pig liver [5]. These authors however only obtained 1 enzymatic form with Km values of 3.1 and 1.8 mM for PAdoP and PAdo2'P, respectively. The potential physiological role of this enzyme in the metabolism of sulphate is also considered. The previously registered number EC 3.1.3.7 could be applied to this activity.

Rat liver ATP-sulfurylase: purification, kinetic characterization, and interaction with arsenate, selenate, phosphate, and other inorganic oxyanions

ATP-sulfurylase (ATP:sulfate adenylyltransferase; EC 2.7.7.4), the first enzyme of the two-step sulfate activation sequence, was purified extensively from rat liver cytosol. The enzyme has a native molecular mass of 122 +/- 12 kDa and appears to be composed of identical 62 +/- 6-kDa subunits. At 30 degrees C and pH 8.0 (50 mM Tris-Cl buffer containing 5 mM excess Mg2+), the best preparations have "forward reaction" specific activities of about 20 and 2 units X mg protein-1 with MoO4(2-) and SO4(2-), respectively. The reverse (ATP synthesis) specific activity is about the same as the forward molybdolysis activity. The kinetic constants under the above conditions are as follows: KmA = 0.21 mM, Kia = 0.87 mM, KmB = 0.18 mM, KmQ = 0.65 microM, Kiq = 0.11 microM, and KmP = 5.0 microM where A = MgATP, B = SO4(2-), Q = APS, and P = total PPi at 5 mM Mg2+. PPi is a mixed-type inhibitor with respect to MgATP and SO4(2-). SeO4(2-) is an alternative inorganic substrate with a Vmax about 20% that of SO4(2-). The product, APSe, is unstable. But in the presence of a sufficient excess of APS kinase, APSe is completely converted to PAPSe. The rate constant for nonenzymatic PAPSe hydrolysis was determined from measurements of the final steady-state reaction rate in the presence of limiting initial SeO4(2-) and a large excess of MgATP, ATP sulfurylase, APS kinase, and the other coupling enzymes and their cosubstrates. The results yielded a k of 2.4 +/- 0.5 X 10(-3) sec-1 (t1/2 ca. 5 min). Phosphate is an effective buffer for enzyme purification and storage but inhibits catalytic activity, particularly at low substrate concentrations. In the presence of buffer levels of Pi, the MgATP reciprocal plot of the SO4(2-)-dependent reaction is concave-up. Inorganic monovalent oxyanions are dead end inhibitors competitive with SO4(2-) and apparently uncompetitive with respect to MgATP. The relative potencies are in the order ClO3- greater than ClO4- greater than FSO3- greater than NO3-. Thiosulfate is also competitive with SO4(2-) but noncompetitive with respect to MgATP. Several divalent oxyanions (MoO4(2-), WO4(2-), CrO4(2-), and HAsO4(2-] promote the enzyme-catalyzed cleavage of MgATP to AMP and MgPPi. The ratio Vmaxf/KmA ranged from 0.7 to 200 for various reactive inorganic substrates. The cumulative results suggest the random binding of MgATP and the inorganic substrate but the ordered release of MgPPi before APS.(ABSTRACT TRUNCATED AT 400 WORDS)

Distribution of 2-naphthol sulphotransferase and its endogenous substrate adenosine 3'-phosphate 5'-phosphosulphate in human tissues

The activity of sulphotransferase towards 2-naphthol and the concentration of its endogenous substrate, adenosine 3'-phosphate 5'-phosphosulphate (PAPS), have been measured in five specimens of human liver, lung, and kidney, and the mucosa from the ileum and the ascending, descending and sigmoid colon. The activity of 2-naphthol sulphotransferase (mean nmol.min-1.mg-1 protein) was 1.82 (liver); 0.034 (kidney); 0.19 (lung); 0.64 (ileum); 0.47 (ascending colon); 0.50 (descending colon); 0.40 (sigmoid colon). The concentration of PAPS (mean nmol.g-1 wet tissue) was 22.6 (liver); 4.8 (kidney); 4.3 (lung); 12.8 (ileum); 8.1 (ascending colon); 7.5 (descending colon); 6.2 (sigmoid colon). The concentration of PAPS and the activity of 2-naphthol sulphotransferase were higher in the liver than in the extrahepatic tissues. There was significant difference between ileum and ascending colon, both the activity of sulphotransferase and the concentration of PAPS being higher in the former. 2-Naphthol sulphotransferase activity and the concentration of PAPS have consistent distribution patterns. Differences between the tissues studied were more marked for sulphotransferase than for its endogenous substrate.

Formation and utilization of the active sulfate donor [35S]3'-phosphoadenosine 5'-phosphosulfate in brain slices: effects of depolarizing agents

The accumulation and utilization of [35S]3'-phosphoadenosine 5'-phosphosulfate (PAPS) were studied in slices from rat cerebral cortex incubated in the presence of inorganic [35S]sulfate. [35S]PAPS levels were directly evaluated after either isolation by ion-exchange chromatography or quantitative enzymatic transfer of its active [35S]sulfate group to an acceptor phenol under the action of added phenolsulfotransferase activity. [35S]PAPS formation was also indirectly followed by incubating slices in the presence of beta-naphthol and measuring the levels of [35S]beta-naphthyl sulfate ([35S]beta-NS). Whereas [35S]PAPS levels rapidly reached a plateau, [35S]beta-NS formation proceeded linearly with time for at least 1 h, an observation indicating that the nucleotide was continuously synthesized and utilized for endogenous sulfation reactions. [35S]PAPS formation in slices was completely and rather potently blocked by 2,6-dichloro-4-nitrophenol (IC50 = 10 microM), an inhibitor of the PAPS-synthesizing enzyme system in a cytosolic preparation. [35S]PAPS accumulation and [35S]beta-NS formation were strongly reduced by depolarizing agents such as potassium or veratridine. At millimolar concentrations, various excitatory amino acids (glutamate, aspartate, cysteate, quisqualate, and homocysteate) also elicited similar effects, whereas kainate and N-methyl-D-aspartate were inactive. This suggests that PAPS synthesis is turned off when cerebral cells are strongly depolarized.

Properties and localization of the sulfate-activating system in rat brain

The formation of the sulfate donor [35S]3'-phosphoadenosine 5'-phosphosulfate (PAPS) from inorganic [35S]sulfate was studied using a novel assay. The assay was based on the quantitative transfer of radioactivity from [35S]PAPS to beta-naphthol under the action of phenolsulfotransferase activity from rat brain cytosol, with the [35S]beta-naphthyl sulfate formed being isolated by polystyrene bead chromatography. This simple assay was validated by comparison of results with those derived from direct assay of [35S]PAPS isolated by either TLC or ion exchange chromatography. [35S]PAPS formation by a high-speed supernatant of rat cerebral cortex occurred with an optimal pH of approximately 7.6, varied linearly with time and protein concentration, and depended on the presence of Mg2+-ATP. The latter could not be replaced by other nucleotides such as GTP, UTP, or CTP, which at 1-5 mM concentrations inhibited the reaction. Mg2+ could not be replaced by Mn2+, which at micromolar concentrations inhibited the reaction. The apparent Km values of Mg2+-ATP (at 0.1 mM [35S]sulfate) and inorganic sulfate (at 5 mM Mg2+-ATP) were 2.7 and 0.2 mM, respectively. These kinetics parameters corresponded to those reported for purified ATP sulfurylase (EC 2.7.7.4), the enzyme responsible for the first step of PAPS synthesis in liver. The product of its reaction, [35S]adenosine 5'-phosphosulfate (APS), could not be detected after incubations, an observation implying that the action of APS kinase was not rate limiting in cerebral extracts tested under the selected experimental conditions. [35S]PAPS formation was detectable in cytosolic fractions from various brain regions, which displayed only limited differences in synthesizing activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Utilization of ascorbate-2-sulfate in fish

Although most vertebrate animals synthesize L-ascorbic acid (C1), some animal species lack the ability to produce L-gulonolactone oxidase and are thus dependent upon a dietary source of vitamin C. Fish are unique among this latter group in that they store a chemically stable form of vitamin C and appear to metabolize this compound differently from other vitamin C-requiring organisms. Ascorbate-2-sulfate (C2) contributes to total body stores of ascorbate, but the commonly used assays for ascorbate concentrations in tissues and body fluids do not generally measure C2. An HPLC assay distinguishes between and measures both C1 and C2. Modification of the less exact but commonly used DNPH method can provide adequate data to estimate total vitamers C, C1, and (by difference) C2. Since vitamin C is a required component of feed for salmonids, catfish, eels, shrimp and carp, use of C2 in feed formulation would provide a bioavailable form of ascorbate which is heat and water stable at pH 4-13.

Properties of the purified APS-kinase from Escherichia coli and Saccharomyces cerevisiae

Adenylylsulphate kinase (EC 2.7.1.25, ATP:adenylylsulphate 3'-phosphotransferase) has been isolated from Escherichia coli and from Saccharomyces cerevisiae. As major steps of purification, affinity chromatography on Sepharose CL 6B ("blue" or "red") and chromatofocusing on polybuffer PBE 94tm were employed. The proteins were obtained in nearly homogeneous state after five chromatographic steps. The isolated enzymes from both sources appeared predominantly to exist as dimers. Upon reduction of the protein with dithiothreitol, it disintegrated into assumingly identical smaller subunits (E. coli rom Mr 90-85,000 to 45-40,000 and S. cerevisiae from 52-49,500 to 28-29,500). Both forms, dimer and monomer were found catalytically active. Preincubation of the isolated enzyme from either source in the presence of thioredoxin plus DTT, reduced glutathione or DTT increased the activity significantly. Treatment of the enzyme with SH-blocking reagents inactivated the enzyme irreversibly as compared to the inactivation caused by oxidants (2,6-dichlorophenol-indophenol, ferricyanide or oxydized glutathione). This oxidant induced inactivation was less pronounced for the fungal enzyme than for the bacterial protein. The enzyme from E. coli required thioredoxin in order to alleviate the GSSG-induced inactivation.

Biochemical aspects of globoid and metachromatic leukodystrophies

Galactosylceramides and sulfogalactosylceramides are characteristic lipids of the myelin sheath. Two genetically determined leukodystrophies are caused by an inability to enzymically hydrolyze these glycolipids. Thus, a deficiency of galactocerebroside beta-galactosidase results in globoid cell leukodystrophy, whereas a reduced activity of arylsulfatase A is responsible for metachromatic leukodystrophy. Besides these disorders, deficiencies of arylsulfatases A, B, C, and other sulfatases have been shown in a distinct condition called "multiple sulfatase deficiency." All of these disorders are fatal and are characterized by marked demyelination and severe mental retardation. The cause of this demyelination is not known. However, cytotoxic galactosylsphingosine and sulfogalactosylsphingosine have been suggested as the agents responsible for this demyelination. Recent immunological studies have also shown that patients with globoid and metachromatic leukodystrophies contain a mutant galactocerebroside beta-galactosidase and arylsulfatase A, respectively. The mutant enzymes have different kinetic properties compared to the enzymes from normal subjects. However, they can cross-react with antibodies to these enzymes. Since partially purified preparations of galactocerebroside beta-galactosidase and homogeneous arylsulfatase A are now available, the possibility of enzyme replacement therapy in globoid and metachromatic leukodystrophies is discussed.