A kinetic comparison of partially purified rat liver Golgi and rat serum galactosyltransferases.

UDP-galactose: N-acetylglucosamine beta-1,4-galactosyltransferase was partially purified from rat liver Golgi membranes and rat serum. The kinetic parameters of the two enzymes isolated by affinity chromatography were compared with each other and with those for commercial bovine milk galactosyltransferase. When N-acetyl-glucosamine was the acceptor the Km values for UDP-galactose were 65,52 and 43 microM for the rat liver Golgi, rat serum and bovine milk enzymes respectively. The Km values for N-acetylglucosamine were 0.33, 1.49 and 0.5 mM for the three enzymes respectively. The Km values for UDP-galactose, with glucose as acceptor in the presence of 1 mg of alpha-lactalbumin, were 23, 9.0 and 60 microM for the three enzymes respectively, and the Km values for glucose were 2.3, 1.8 and 2.0 mM respectively. The effects of alpha-lactalbumin in both the lactosamine synthetase and lactose synthetase reactions were similar. The activation energies were 94.0 kJ/mol (22.5 kcal/mol) and 96.0 kJ/mol (22.9 kcal/mol) for the Golgi and serum enzymes respectively. Although some differences in Km values were observed between the rat liver Golgi and serum enzymes, the values obtained suggest a high degree of similarity between the kinetic properties of the three galactosyltransferases.     

Purification and characterization of bile salt sulfotransferase from human liver

Bile salt sulfotransferase, the enzyme responsible for the formation of bile salt sulfate esters, was purified extensively from normal human liver. The purification procedure included DEAE-Sephadex chromatography, taurocholate-agarose affinity chromatography, and preparative isoelectrofocusing. The final preparation had a specific activity of 18 nmol min-1 mg protein-1, representing a 760-fold purification from the cytosol fraction with a overall yield of 15%. The human enzyme has a Mr of 67,000 and a pI of 5.2. DEAE-Sephadex chromatography of the cytosol fraction revealed only a single species of activity. The limiting Km for the sulfuryl donor, 3'-phosphoadenosine-5'-phosphosulfate (PAPS), is 0.7 microM. The limiting Km for the sulfuryl acceptor, glycolithocholate (GLC), is 2 microM. Reciprocal plots were intersecting. Product inhibition studies established that adenosine 3',5'-diphosphate (PAP) was competitive with PAPS (Ki = 0.2 microM) and noncompetitive with respect to GLC. GLC sulfate was competitive with GLC (Ki = 2.2 microM) and noncompetitive with respect to PAPS. Also, 3-ketolithocholate, a dead-end inhibitor, was competitive with GLC (Ki = 0.6 microM) and noncompetitive with respect to PAPS. Iso-PAP (the 2' isomer of PAP) was competitive with PAPS (Ki = 0.3 microM) and noncompetitive with GLC. The cumulative results of the steady-state kinetics experiments point to a random mechanism for the binding of substrates and release of products. The purified enzyme displays no activity toward estrone, testosterone, or phenol. Among the reactive substrates tested, the Vmax/Km values are in the order GLC greater than 3-beta OH-5-cholenic acid greater than glycochenodeoxycholate greater than glycocholate. p-Chloromercuribenzoate inactivated the enzyme. Either PAPS or GLC protected against inactivation, suggesting the presence of a sulfhydryl group at the active site.     

Distribution, purification and characterization of rat intestinal UDPgalactose: N-acetylglucosaminyl(beta 1----4)galactosyltransferase

Rat intestinal UDPgalactose: N-acetylglucosaminyl(beta 1----4)galactosyltransferase activity was studied as to its intestinal and villus-to-crypt distribution, and then purified and characterized. Rapid UDPgalactose hydrolysis was noted in the duodenum and jejunum; little to no breakdown was detected in the distal ileum, cecum and proximal colon. Product analysis suggested that UDPgalactose hydrolysis was due to nucleotide-sugar pyrophosphatase and galactose-1-phosphate phosphatase activities; ileum appeared to have little of the first activity and none of the latter. An aboral gradient of galactosyltransferase activity was noted, activity being 3-4-fold higher in the ileum, cecum and proximal colon. Total homogenate exogenous acceptor galactosyltransferase activities showed no villus-crypt differences but activity measured with intact isolated cells demonstrated higher activity with crypt cells; this was particularly evident in the ileum. Galactosyltransferase activity was purified from ileal-colonic mucosa. An over 4000-fold purification with 75 percent yield was achieved. Only one band of approx. 70-75 kDa was noted on sodium dodecyl sulfate polyacrylamide electrophoresis. As with other eukaryotic galactosyltransferase activities, there was an absolute requirement for Mn2+; the concentration required for half maximal activity was only 2.5 microM and higher concentrations did not inhibit. The Km for UDPgalactose was 30 microM.     

Human plasma uridine diphosphate galactose-glycoprotein galactosyltransfertase. Purification, properties and kinetics of the enzyme-catalysed reaction.

The soluble galactosyltransferase of human plasma catalysed the transfer of galactose from UDP-galactose to high- and low-molecular-weight derivatives of N-acetylglucosamine, forming a beta-1-4 linkage. The enzyme was purified by using (NH4)2SO4 precipitation and affinity chromatography on an alpha-lactalbumin-Sepharose column. The galactosyltransferase was maximally bound to this column in the presence of N-acetylglucosamine, and the enzyme was eluted by omitting the amino sugar from the developing buffer. The molecular weight of the enzyme was estimated to be 85000 by gel filtration. The assay conditions for optimum enzymic activity was 30 degrees C and pH7.5. Mn2+ ion was found to be an absolute requirement for transferase activity. The Km for Mn2+ was 0.4 mM and that for the substrate, UDP-galactose, was 0.024 mM. The Km for the acceptors was 0.21 mM for alpha1-acid glycoprotein and 3.9 mM for N-acetylglucosamine. In the presence of alpha-lactalbumin, glucose became a good acceptor for the enzyme and had a Km value of 2.9 mM. Results of the kinetic study indicated that the free enzyme reacts with Mn2+ under conditions of thermodynamic equilibrium, and the other substrates are added sequentially.     

Human placental 3 beta-hydroxy-5-ene-steroid dehydrogenase and steroid 5----4-ene-isomerase: purification from microsomes, substrate kinetics, and inhibition by product steroids

In human pregnancy, placental 3 beta-hydroxy-5-ene-steroid dehydrogenase and steroid 5----4-ene-isomerase produce progesterone from pregnenolone and metabolize fetal dehydroepiandrosterone sulfate to androstenedione, an estrogen precursor. The enzyme complex was solubilized from human placental microsomes using the anionic detergent, sodium cholate. Purification (500-fold, 3.9% yield) was achieved by ion exchange chromatography (Fractogel-TSK DEAE 650-S) followed by hydroxylapatite chromatography (Bio-Gel HT). The purified enzyme was detected as a single protein band in sodium dodecylsulfate-polyacrylamide gel electrophoresis (monomeric Mr = 19,000). Fractionation by gel filtration chromatography at constant specific enzyme activity supported enzyme homogeneity and determined the molecular mass (Mr = 76,000). The dehydrogenase and isomerase activities copurified. Kinetic constants were determined at pH 7.4, 37 degrees C for the oxidation of pregnenolone (Km = 1.9 microM, Vmax = 32.6 nmol/min/mg) and dehydroepiandrosterone (Km = 2.8 microM, Vmax = 32.0 nmol/min/mg) and for the isomerization of 5-pregnene-3,20-dione (Km = 9.7 microM, Vmax = 618.3 nmol/min/mg) and 5-androstene-3,17-dione (Km = 23.7 microM, Vmax = 625.7 nmol/min/mg). Mixed substrate analyses showed that the dehydrogenase and isomerase reactions use the appropriate pregnene and androstene steroids as alternative, competitive substrates. Dixon analyses demonstrated competitive inhibition of the oxidation of pregnenolone and dehydroepiandrosterone by both product steroids, progesterone and androstenedione. The enzyme has a 3-fold higher affinity for androstenedione than for progesterone as an inhibitor of dehydrogenase activity. Based on these competitive patterns of substrate utilization and product inhibition, the pregnene and androstene activities of 3 beta-hydroxy-5-ene-steroid dehydrogenase and steroid 5----4-ene-isomerase may be expressed at a single catalytic site on one protein in human placenta.     

Characterization and membrane organization of beta 1----3- and beta 1----4-galactosyltransferases from human colonic adenocarcinoma cell lines Colo 205 and SW403: basis for preferential synthesis of type 1 chain lacto-series carbohydrate structures

Evidence indicates that activation of a beta 1----3N-acetylglucosaminyltransferase is responsible for accumulation of large quantities of lacto-series tumor-associated antigens in human colonic adenocarcinomas. Expression of type 1 and 2 core chain derivatives characterize human colonic adenocarcinomas, whereas normal adult colonic epithelial cells express detectable quantities of only type 1 chain derivatives. The basis for preferential synthesis of type 1 chain lacto-series carbohydrate structures characteristic of normal colonic mucosa and human colonic adenocarcinoma Colo 205 cells has been studied. The beta 1----3- and beta 1----4galactosyltransferase enzymes associated with synthesis of type 1 and 2 core chain structures, respectively, have been separated from a Triton X-100 solubilized membrane fraction of Colo 205 cells by chromatography on an alpha-lactalbumin-Sepharose column and their properties studied. Optimal transfer of beta 1----3-linked galactose to acceptor Lc3 occurred in the presence of 0.1% Triton CF-54 with Triton X-100 providing 75% of maximal activity. The enzyme was active over a broad pH range from 6.5 to 7.5 and had a near absolute requirement for Mn2+. The Km values for donor UDPgalactose and acceptor Lc3 were determined to be 48 and 13 microM, respectively. In contrast, the beta 1----4galactosyltransferase required taurodeoxycholate for maximal activity and the Km for Lc3 was found to be 20-fold higher than that for the beta 1----3-specific enzyme under the same assay conditions. Studies with membrane-bound beta 1----3- and beta 1----4galactosyltransferases as found in Golgi-rich membrane fractions of SW403 and Colo 205 adenocarcinoma cells showed that preferential synthesis of type 1 chain structures occurs under conditions similar to those in vivo for biosynthesis of lacto-series core chains. The results suggest that both the higher affinity of the beta 1----3galactosyltransferase for acceptor Lc3 and the membrane organizational features result in preferential synthesis of type 1 chain structures.     

Identification of UDP-galactose: lactose (lactosylceramide) alpha-4 and beta-3 galactosyltransferases in human kidney

Two galactosyltransferases were identified in human kidney microsomes which both transfer galactose from UDP Gal to lactose as well as to lactosylceramide. Using a solubilized and a partially purified enzyme preparation sufficient product could be obtained for detailed structural analysis. The trisaccharide products were isolated by gel permeation chromatography and separated by preparative high performance thin layer chromatography. The anomeric configuration of the transferred galactose was determined by specific glycosidase digestion and the linkage was identified by methylation and gas-liquid-chromatography. The glycolipid products were not separated but analyzed directly, before and after alpha or beta galactosidase digestion, by methylation, hydrolysis and thin layer chromatography. Into both acceptor substrates galactose was incorporated in alpha 1-4 (30%) and beta 1-3 (70%) linkages. The alpha 1-4 galactosyltransferase is responsible for the synthesis of the Pk antigen Gal alpha 1-4 Gal beta 1-4 Glc-ceramide in human kidney. The beta 1-3 galactosyltransferase has not previously been identified.     

Rapid affinity chromatographic purification of human lung and kidney angiotensin-converting enzyme with the novel N-carboxyalkyl dipeptide inhibitor N-[1(S)-carboxy-5-aminopentyl]glycylglycine

Human angiotensin-converting enzyme has been purified, in a single chromatographic step, using a novel N-carboxyalkyl dipeptide CA-GlyGly (N-[1(S)-carboxy-5-aminopentyl]glycylglycine) synthesised in our laboratory. CA-GlyGly is a weak competitive inhibitor, Ki = 0.18 mM, and its inhibitory profile is markedly pH-dependent. Human lung and kidney angiotensin-converting enzyme were solubilised with Triton X-100 and after ammonium sulphate fractionation the crude extract was applied to a column containing CA-GlyGly coupled to agarose via a 2.8 nm spacer group. Electrophoretically pure human angiotensin-converting enzyme could be eluted by raising the pH of the chromatography buffer from 7.50 to 9.50. The specific activity of human angiotensin-converting enzyme purified from lung was 104 units/mg, while that from kidney was 88 units/mg. Molecular weight for both enzymes was estimated to be 160,000. The Km with respect to hippuryl-L-histidyl-L-leucine was 1.9 mM in the case of lung angiotensin-converting enzyme and 1.7 mM in that of kidney angiotensin-converting enzyme, while for the substrate angiotensin I Km values were 62 microM and 76 microM, respectively. Hydrolysis of either substrate was chloride-dependent and both enzymes were strongly inhibited by captopril.     

Purification and characterization of a high molecular weight type 1 phosphoprotein phosphatase from the human erythrocyte

The major Mn2+-activated phosphoprotein phosphatase of the human erythrocyte has been purified to homogeneity from the cell hemolysate. It is sensitive to both inhibitors 1 and 2 of rabbit skeletal muscle, preferentially dephosphorylates the beta subunit of the phosphorylase kinase, and dephosphorylates a broad range of substrates including phosphorylase a, p-nitro-phenyl phosphate, phosphocasein, the regulatory subunit of cyclic AMP-dependent protein kinase, and both spectrin (Km = 10 microM) and pyruvate kinase (Km = 18 microM) purified from the human erythrocyte. The purified enzyme is stimulated by Mn2+ and to a lesser extent by higher concentrations of Mg2+. The purification procedure was selected to avoid any change in molecular weight, hence subunit composition, between the crude and purified enzyme. Maintenance of the original structure is demonstrated by non-denaturing gel electrophoresis and gel filtration chromatography. Gel filtration of the purified holoenzyme shows a single active component with a Stokes radius of 58 A at a molecular weight position of 180,000. Sedimentation velocity in a glycerol gradient gives a value of 6.1 for S20, w. Together these data indicate a molecular weight of about 135,000. Two bands of equal intensity appear on sodium dodecyl sulfate-gel electrophoresis at molecular weights of 61,700 and 36,300, suggesting a subunit composition of two 36,000 and one 62,000 subunits. The 36-kDa catalytic subunit can be isolated by freezing and thawing the holoenzyme or by hydrophobic chromatography of the holoenzyme. The catalytic subunit shows unchanged substrate and inhibitor specificity but altered metal ion activation.     

UDP-rhamnose:flavanone-7-O-glucoside-2'-O-rhamnosyltransferase. Purification and characterization of an enzyme catalyzing the production of bitter compounds in citrus

The rhamnosyltransferase catalyzing the production of the bitter flavanone-glucosides, naringin and neohesperidin, was purified to homogeneity. The enzyme catalyzes the transfer of rhamnose from UDP-rhamnose to the C-2 hydroxyl group of glucose attached via C-7-O- of naringenin or hesperetin. To our knowledge this is the first complete purification of a rhamnosyl-transferase. The enzyme from young pummelo leaves was purified greater than 2,700-fold to a specific activity of over 600 pmol/min/mg of protein by sequential column chromatographies on Sephacryl S-200, reactive green 19-agarose, and Mono-Q. The enzyme was selectively eluted from the green dye column with only three other proteins by a pulse of the substrate hesperetin-7-O-glucoside followed by UDP. The rhamnosyltransferase is monomeric (approximately 52 kDa) by gel filtration and electrophoresis. The enzyme rhamnosylates only with UDP-rhamnose. Flavonoid-7-O-glucosides are usable acceptors but 5-O-glucosides or aglycones are not. It is inhibited by 10 microM UDP, its end product, but not by naringin or neohesperidin. Several flavonoid-aglycones at 100 microM inhibited the rhamnosyltransferase; UDP-sugars did not. The Km for UDP-rhamnose was similar with prunin (1.3 microM) and hesperetin-7-O-glucoside (1.1 microM) as substrate. The affinity for the natural acceptor prunin (Km = 2.4 microM) was much higher than for hesperetin-7-O-glucoside (Km = 41.5 microM). The isolation of the gene may enable its use in genetic engineering directed to modifying grapefruit bitterness.     

Stimulation of bovine milk galactosyltransferase activity by bovine colostrum N-acetylglucosaminyltransferase I

Purified bovine milk galactosyltransferase was stimulated by purified bovine colostrum N-acetylglucosaminyltransferase I by more than 10-fold. Only slight stimulation of the N-acetylglucosaminyltransferase I by galactosyltransferase was observed. Heat inactivation destroyed the ability of the N-acetylglucosaminyltransferase I to stimulate the galactosyltransferase. The stimulation of galactosyltransferase was accompanied by a decrease in Km of this enzyme from 9.7 to 3.3. mM and an increase in Vmax from 1.87 to 3.71 nmol galactose transferred/min per mg galactosyltransferase when GlcNAc was the substrate. When the Km for UDPgalactose was determined, it increased from 0.19 to 0.42 mM in the presence of N-acetylglucosaminyltransferase I and the Vmax increased from 0.66 to 2.76 nmol galactose transferred/min per mg galactosyltransferase. In phosphatidylcholine vesicles, no effect on Km values with GlcNAc as substrate was noted, while an increase in the Km of UDPgalactose was observed. The Vmax values were generally higher in the lipid vesicles. Complex formation between galactosyltransferase and N-acetylglucosaminyltransferase I was demonstrated both by glycerol density gradient centrifugation and Bio-Gel P-100 column chromatography. An approximate molecular weight for the complex was obtained on a calibrated Sephadex G-200 column and found to be about 75 000, consistent with a 1:1 complex. The stimulation of galactosyltransferase involved the N-acetyllactosamine synthetase activity of this enzyme and not the lactose synthetase activity, since the latter activity was only slightly affected. Since N-acetylglucosaminyltransferase I is not involved in the lactose synthetase reaction, the stimulation is consistent with the known biosynthetic role of N-acetylglucosaminyltransferase I in the biosynthesis of asparagine-linked oligosaccharides.     

Characterization of the sialate-7(9)-O-acetyltransferase from the microsomes of human colonic mucosa

Sialic acids present on human colonic mucins are highly O-acetylated, however, little is known about the underlying enzymatic activity required for O-acetylation in this tissue. Here we report on the substrate specificity, subcellular localization and characterization of the sialate-7(9)-O-acetyltransferase in normal human colonic mucosa. Using CMP-Neu5Ac, the most efficient acceptor substrate of all those tested, the enzymatic activity was found to be optimal at 37 degrees C, with a pH optimum of 7.0. Activity was also found to be dependent on protein, CMP-Neu5Ac (Km: 59.2 microM) and AcCoA (Km: 6.1 microM) concentrations, as well as membrane integrity. The enzyme's activity could be inhibited by CoA with a Ki of 11.9 microM. In addition, enzymatic activity was found to be localized in the Golgi-enriched membrane fraction. The nature of the O-acetylated products formed were verified with the aid of chromatographic and enzymatic techniques. The main product was 9-O-acetylated Neu5Ac, with a significant amount of oligo-O-acetylated Neu5Ac also being detected. The utilization of CMP-Neu5Ac as the acceptor substrate was confirmed by the isolation and characterization of the putative product, CMP-Neu5,9Ac2, using ion-exchange chromatography. The ability of CMP-Neu5,9Ac2 to act as a sialic acid donor for sialyltransferases represents the conclusive demonstration for the formation of CMP-Neu5,9Ac2.     

The distribution and partial characterization of UDPgalactose: N-acetylgalactosamine mucin galactosyltransferase activity from rat small intestine and its sensitivity to Zn2+

UDPgalactose: N-acetylgalactosamine mucin galactosyltransferase activity of the rat intestine was studied and purified using asialo-ovine submaxillary mucin as the acceptor substrate and inhibitors to suppress UDPgalactose breakdown by pyrophosphatase activities particularly prevalent in the duodenal-jejunal regions. Despite adequate suppression of UDPgalactose breakdown, significant intestinal region differences of mucin galactosyltransferase activity were observed. Elevations of activity were observed in the duodenum and distal ileum of the small intestine and the cecum and proximal colon; these elevations in activity correspond to areas of increased mucin production. Similarly, mucin galactosyltransferase activity of duodenal cells isolated along a crypt-to-villus axis showed a moderate increase (67.7%) in activity associated with cells in the crypt region. Small intestine mucin galactosyltransferase activity was purified 800-fold using a series of ion exchange (DEAE-Sepharose), gel filtration (S-200 Sephacryl) and affinity chromatographic steps to isolate the mucin galactosyltransferase activity from a Triton X-100/Nonidet P-40 extract of homogenized cells obtained by scraping everted intestines. The partially purified enzyme showed two distinct protein bands of 81.5 and 50 kDa and a faint band at 53.3 kDa. Kinetic analysis gave an apparent Km of 152 microM for UDPgalactose. The enzyme showed optimal activity with Mn2+ (20 mM) and partial activities using a number of other divalent cations. Higher concentrations of Mn2+ were slightly inhibitory. Mucin galactosyltransferase activity was inhibited by more then 90% in the presence of Zn2+ (4 mM) and this inhibition could not be reversed by additional Mn2+. Addition of Zn2+ (4 mM) to assays containing Mn2+ (20 mM) did not cause appreciable UDPgalactose breakdown, as measured by high-voltage paper electrophoresis, suggesting that Zn2+ inhibition is not a result of pyrophosphatase activation. In addition, Zn2+ does not appear to activate a protease or glycosidase activity in the partially purified enzyme preparation which could hydrolyze the galactosylated product prior to isolation.     

Purification and kinetic characterization of a dopamine-sulfating form of phenol sulfotransferase from human brain

The kinetic and biochemical properties of a purified, monoamine-sulfating form of phenol sulfotransferase (M-PST) from human brain are described. M-PST activity was separated and purified from phenol-sulfating activity by anion-exchange chromatography on DEAE-cellulose and subsequently purified on AffiGel Blue and Sephacryl S-200, routinely giving a final purification of over 20 000-fold, with approximately a 3% yield. The molecular weight of the active species, as estimated by gel filtration chromatography, was 250 000. The purified enzyme was inhibited by NaCl (50% at 325 mM) and showed an optimum for dopamine sulfation at pH 7.0. Of the monoamine substrates examined, 4-methoxytyramine was the most extensively sulfated at 20 microM, while at higher substrate concentrations (200 microM), tyramine was the apparent preferred substrate. Kinetic analysis demonstrated that sulfation by M-PST proceeds via an ordered, bisubstrate reaction mechanism, where 3'-phosphoadenosine 5'-phosphosulfate (PAPS) is the leading substrate. True Km values for dopamine and PAPS were 2.9 and 0.35 microM, respectively. The product inhibitor 3'-phosphoadenosine 5'-phosphate possessed a Ki of 0.07 microM, while the dead-end inhibitor ATP exhibited a Ki of 170 microM.     

Induction of thymidine kinase and DNase in varicella-zoster virus-infected cells and kinetic properties of the virus-induced thymidine kinase.

Thymidine kinase (TK), DNA polymerase, and DNase activities were induced in human foreskin fibroblasts after varicella-zoster virus infection. The induced TK and DNase activities have electrophoretic mobilities different from the corresponding host enzymes. Varicella-zoster virus-induced TK was purified and separated from the host enzyme by affinity column chromatography. This enzyme has been shown to have a broader substrate specificity with respect to either the phosphate donor or acceptor as compared with human cytoplasmic and mitochondrial TKs. The best phosphate donor is ATP, with a Km of 16 microM. The Km values of thymidine, deoxycytidine, and 5-propyl deoxyuridine were estimated to be 0.4, 180, and 0.8 microM, respectively. The Ki values for several analogs of thymidine such as 5-iododeoxyuridine, arabinofuranosylthymine, 5-ethyl deoxyuridine, and 5-cyanodeoxyuridine were also examined. TTP acted as a noncompetitive inhibitor with respect to thymidine with a Ki of 5 microM. The kinetic behavior of varicella-zoster virus-induced TK is different from human cytoplasmic, human mitochondrial, and herpes simplex virus type 1- and 2-induced TKs.     

Purification and characterization of prephenate aminotransferase from Anchusa officinalis cell cultures

Prephenate aminotransferase (PAT) from rosmarinic acid-producing cell cultures of Anchusa officinalis has been purified to apparent electrophoretic homogeneity using a combination of high-performance anion-exchange, chromatofocusing, and gel filtration chromatography. The purified enzyme has a native molecular weight of 220,000 and subunit molecular weights of 44,000 and 57,000, indicating a possible alpha 2 beta 2 subunit structure. The purified PAT displays high affinity for prephenate (Km = 80 microM) but could also utilize other aromatic alpha-keto acids at less than 20% the rate with prephenate. L-Aspartate (Km = 80 microM) is about three times as effective as L-glutamate as amino-donor substrate. Anchusa PAT is not subject to feedback inhibition from L-phenylalanine or tyrosine, but its activity is affected by a rosmarinic acid metabolite, 3,4-dihydroxyphenyllactic acid.     

Pyruvate:quinone oxidoreductase from Corynebacterium glutamicum: purification and biochemical characterization

Pyruvate:quinone oxidoreductase catalyzes the oxidative decarboxylation of pyruvate to acetate and CO2 with a quinone as the physiological electron acceptor. So far, this enzyme activity has been found only in Escherichia coli. Using 2,6-dichloroindophenol as an artificial electron acceptor, we detected pyruvate:quinone oxidoreductase activity in cell extracts of the amino acid producer Corynebacterium glutamicum. The activity was highest (0.055 +/- 0.005 U/mg of protein) in cells grown on complex medium and about threefold lower when the cells were grown on medium containing glucose, pyruvate, or acetate as the carbon source. From wild-type C. glutamicum, the pyruvate:quinone oxidoreductase was purified about 180-fold to homogeneity in four steps and subjected to biochemical analysis. The enzyme is a flavoprotein, has a molecular mass of about 232 kDa, and consists of four identical subunits of about 62 kDa. It was activated by Triton X-100, phosphatidylglycerol, and dipalmitoyl-phosphatidylglycerol, and the substrates were pyruvate (kcat=37.8 +/- 3 s(-1); Km=30 +/- 3 mM) and 2-oxobutyrate (kcat=33.2 +/- 3 s(-1); Km=90 +/- 8 mM). Thiamine pyrophosphate (Km=1 microM) and certain divalent metal ions such as Mg2+ (Km=29 microM), Mn2+ (Km=2 microM), and Co2+ (Km=11 microM) served as cofactors. In addition to several dyes (2,6-dichloroindophenol, p-iodonitrotetrazolium violet, and nitroblue tetrazolium), menadione (Km=106 microM) was efficiently reduced by the purified pyruvate:quinone oxidoreductase, indicating that a naphthoquinone may be the physiological electron acceptor of this enzyme in C. glutamicum.     

Purification, product characterization and kinetic properties of lipoxygenase from olive fruit (Olea europaea L.).

Lipoxygenase from olive fruit was purified to homogeneity for the first time after differential centrifugations and by hydrophobic chromatography. The enzyme had a molecular mass of 98 kDa and exhibited a maximal activity at pH 6. Lipoxygenase had a better affinity for linoleic acid (Km=82.44 microM) than for linolenic acid (Km = 306.26 microM). It is inhibited by linoleate:oxygen oxidoreductase (LOX) inhibitors like nordihydroguaiaretic acid (NDGA) or propyl gallate. The reaction product was 13-hydroperoxy octadecadienoic acid when linoleic acid was used as substrate.     

Human placental 3 beta-hydroxy-5-ene-steroid dehydrogenase and steroid 5----4-ene-isomerase: purification from mitochondria and kinetic profiles, biophysical characterization of the purified mitochondrial and microsomal enzymes

In human placenta, 3 beta-hydroxy-5-ene-steroid dehydrogenase and steroid 5----4-ene-isomerase, an enzyme complex found in microsomes and mitochondria, synthesizes progesterone from pregnenolone and androstenedione from fetal dehydroepiandrosterone sulfate. The dehydrogenase and isomerase activities of the mitochondrial enzyme were copurified (733-fold) using sequential cholate solubilization, ion exchange chromatography (DEAE-Toyopearl 650S), and hydroxylapatite chromatography (Bio-Gel HT). Enzyme homogeneity was demonstrated by a single protein band in SDS-polyacrylamide gel electrophoresis (monomeric Mr = 41,000), gel filtration at constant specific enzyme activity (Mr = 77,000), and a single NH2-terminal sequence. Kinetic constants were determined for the oxidation of pregnenolone (Km = 1.6 microM, Vmax = 48.6 nmol/min/mg) and dehydroepiandrosterone (Km = 2.4 microM, Vmax = 48.5 nmol/min/mg) and for the isomerization of 5-pregnene-3,20-dione (Km = 9.3 microM, Vmax = 914.2 nmol/min/mg) and 5-androstene-3,17-dione (Km = 27.6 microM, Vmax = 888.4 nmol/min/mg. Mixed substrate studies showed that the dehydrogenase and isomerase activities utilize their respective pregnene and androstene substrates competitively. Dixon analysis demonstrated that the product steroids, progesterone and androstenedione, are competitive inhibitors of the C-21 and C-19 dehydrogenase activities. Enzyme purified from mitochondria and microsomes had similar kinetic profiles with respect to substrate utilization, product inhibition, and cofactor (NAD+) reduction (mean Km +/- SD using C-19 and C-21 dehydrogenase substrates = 26.4 +/- 0.8 microM, mean Vmax = 73.2 +/- 1.3 nmol/min/mg). Pure enzyme from both organelles exhibited identical biophysical properties in terms of molecular weight and subunit composition, pH optima (pH 9.8, dehydrogenase; pH 7.5, isomerase), temperature optimum (37 degrees C), stability in storage and solution, effects of divalent cations, and the single NH2-terminal sequence of 27 amino acids. These results suggest that the mitochondrial and microsomal enzymes are the same protein localized in different organelles.     

Purification and kinetic characterization of a phenol-sulfating form of phenol sulfotransferase from human brain

The identification of three forms of phenol sulfotransferase (PST) in human brain and the subsequent purification and kinetic characterization of a phenol-sulfating form of the enzyme are described. Two forms of PST which were capable of conjugating phenol and a third form which sulfated dopamine were resolved from one another using DEAE-cellulose chromatography. One of the phenol-sulfating forms (P1-PST) was subsequently purified on Affi-Gel blue and Sephacryl S-200, giving a final purification of almost 390-fold, with an overall yield of approximately 5%. The purified enzyme was sensitive to NaCl and showed an optimum for phenol conjugation at pH 8.5. Kinetic analysis demonstrated that sulfation by P1-PST proceeds via a sequential ordered, bi-substrate reaction mechanism, where 3'-phosphoadenosine-5'-phosphosulfate (PAPS) is the leading substrate. The true Km and Kia values for PAPS were both 0.35 microM, while the true Km value for phenol was 2.8 microM.