A flavonol sulfotransferase (EC 2.8.2.-), which catalyzes the transfer of the sulfate group from 3'-phosphoadenosine 5'-phosphosulfate to the 3-hydroxyl group of flavonol aglycones, has been purified to apparent homogeneity from Flaveria chloraefolia. The specific activity of flavonol 3-sulfotransferase was enriched 2000-fold, as compared with the homogenate, with a recovery of 9%. The molecular mass of the native and denatured enzyme was found to be 34.5 kDa, suggesting that the active from of the enzyme is a monomer. The enzyme exhibited expressed specificity for position 3 of flavonol aglycones, showed two activity optima at pH 6.0 and 8.5, did not require divalent cations, and was not inhibited by either EDTA or sulfhydryl group reagents. The results of substrate interaction kinetics and product inhibition are consistent with an Ordered Bi Bi mechanism where 3'-phosphoadenosine 5'-phosphosulfate is the first substrate to bind to the enzyme and 3'-phosphoadenosine 5'-phosphate is the final product to be released. The amino acid sequence of two peptides representing 17 and 33 amino acids showed no significant sequence similarity with the amino acid sequences reported for animal sulfotransferases. Antibodies raised against F. chloraefolia 3-sulfotransferase were found to cross-react with the 3'- and 4'-sulfotransferase activities of the same plant, suggesting that the three enzymes are structurally related. (+info)
Purification and initial characterization of peptidyl-tRNA hydrolase from rabbit reticulocytes.
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We have identified an activity in rabbit reticulocyte lysate as peptidyl-tRNA hydrolase, based upon its ability to hydrolyze native reticulocyte peptidyl-tRNA, isolated from polyribosomes, and N-acylaminoacyl-tRNA, and its inability to hydrolyze aminoacyl-tRNA, precisely the same substrate specificity previously reported for peptidyl-tRNA hydrolase from bacteria or yeast. The physiological role of the reticulocyte enzyme may be to hydrolyze and recycle peptidyl-tRNA that has dissociated prematurely from elongating ribosomes, as suggested for the bacterial and yeast enzymes, since reticulocyte peptidyl-tRNA hydrolase is completely incapable of hydrolyzing peptidyl-tRNA that is still bound to polyribosomes. We have purified reticulocyte peptidyl-tRNA hydrolase over 5,000-fold from the postribosomal supernatant with a yield of 14%. The purified product shows a 72-kDa band upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis that has co-purified with enzyme activity and comprises about 90% of the total stained protein, strongly suggesting that the 72-kDa protein is the enzyme. Sucrose density gradient analysis indicates an apparent molecular mass for the native enzyme of 65 kDa, implying that it is a single polypeptide chain. The enzyme is almost completely inactive in the absence of a divalent cation: Mg2+ (1-2 mM) promotes activity best, Mn2+ is partly effective, and Ca2+ and spermidine are ineffective. The hydrolase shows a Km of 0.60 microM and Vmax of 7.1 nmol/min/mg with reticulocyte peptidyl-tRNA, a Km of 60 nM and Vmax of 14 nmol/min/mg with Escherichia coli fMet-tRNA(fMet), and a Km of 100 nM and Vmax of 2.2 nmol/min/mg with yeast N-acetyl-Phe-tRNA(Phe). The enzyme has a pH optimum of 7.0-7.25, it is inactivated by heat (60 degrees C for 5 min), and its activity is almost completely inhibited by pretreatment with N-ethylmaleimide or incubation with 20 mM phosphate. The fact that the enzyme hydrolyzes E. coli but not yeast or reticulocyte fMet-tRNA(fMet) may be explained, at least in part, by structural similarities between prokaryotic tRNA(fMet) and eukaryotic elongator tRNA that are not shared by eukaryotic tRNA(fMet). (+info)
Immunopurified 25-hydroxyvitamin D 1 alpha-hydroxylase and 1,25-dihydroxyvitamin D 24-hydroxylase are closely related but distinct enzymes.
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The chick kidney mitochondrial cytochrome P-450 1,25-dihydroxyvitamin D3 24-hydroxylase was partially purified by sequential polyethylene glycol precipitation, aminohexyl-Sepharose 4B, and hydroxylapatite chromatography. The specific activity of the final preparation, when reconstituted with NADPH, adrenodoxin, and adrenodoxin reductase, was 245 pmol/min/mg of protein or 0.56 pmol/min/pmol of P-450. The specific cytochrome P-450 content was 0.45-0.73 nmol/mg of protein. BALB/c mice immunized with this preparation developed serum polyclonal antibodies to the 24-hydroxylase, as demonstrated by immunoprecipitation. Splenic lymphocytes from an immunized mouse were fused with myeloma NSI/1-Ag-4-1 cells, and hybridomas secreting monoclonal antibodies to the 24-hydroxylase were detected by immunoprecipitation. The hybridoma lines were cloned by limiting dilution and further characterized as IgG1, IgG3, and IgM subclasses. In one-dimensional immunoblots of soluble 24-hydroxylase preparations, the monoclonal antibodies revealed a single band with an apparent molecular weight of 59,000. The monoclonal antibodies did not cross-react with cytochrome P-450s from other species but immunoprecipitated and immunoblotted a soluble chick renal mitochondrial 25-hydroxyvitamin D3 1 alpha-hydroxylase preparation, demonstrating the close similarity of these two hydroxylases. These antibodies were coupled to Sepharose CL-4B and used to isolate to homogeneity the two enzymes from chick kidney mitochondria. Amino-terminal sequences and amino acid composition data demonstrate that these enzymes are different but homologous. (+info)
Purification of group C streptococcal extracellular antigens detected with naturally occurring human antibodies: isolation of streptokinase and two previously undescribed antigens.
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Twelve antigens were detected in crude group C streptococcal extracellular concentrates, using naturally occurring antibodies in normal human gamma globulin. These group C streptococcal antigens all appeared to be present in crude group A streptococcal extracellular concentrates, although the latter contained additional antigens reactive with the human antibodies. Systematic purification procedures were established for the isolation of the group C streptococcal antigens by a sequence of salting out, hydroxylapatite chromatography, Sephadex G-100 gel filtration, and isoelectric focusing. With such procedures, three of the group C streptococcal antigens were isolated in a relatively pure state. One of the purified antigens was identified as streptokinase on the basis of its fibrinolytic potency, its reaction of identity with two purified streptokinase fractions obtained from other sources, and its high titer in immunodiffusion assays. The most highly purified streptokinase fractions, derived from the 0.1 M sodium phosphate hydroxylapatite eluate, revealed a plasmin-inhibiting effect at high concentrations of streptokinase. This was not seen in the purified streptokinase of equivalent functional and immunological purity that was derived from the 0.2 M sodium phosphate hydroxylapatite peak. Two other streptococcal antigens were also isolated to a high degree during the course of the above study. These were designated antigens X and Y and were found to be unrelated immunologically to each other or to streptokinase. Their isoelectric points were 6.7 and 8.8, respectively, and both were present in group A streptococcal concentrates. Esterase activity was found to be widely distributed in almost all of the fractions obtained in the various purification steps, indicating a high degree of heterogeneity of the streptococcal enzyme. Histochemical staining techniques applied to the immune precipitates formed with human antibodies indicated that none of the antigens detected in crude group C and group A streptococcal concentrates possessed catalase, glucuronidase, glucosaminidase, acid or alkaline phosphatase, arylsulfatase, leucineaminopeptidase, or chymotrypsin enzymatic activities. (+info)
Purification and characterization of protein kinase C from the nematode Caenorhabditis elegans.
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Protein kinase C (PKC) of Caenorhabditis elegans was identified by enzymatic activity and [3H]phorbol 12,13-dibutyrate binding after DEAE-Sephacel column chromatography of a crude cytosolic extract. Ca(2+)-dependent activation of nematode PKC was observed in the presence of phosphatidylserine. The enzyme was maximally activated by 1,2-dioleoylglycerol or phorbol 12-myristate 13-acetate in the presence of phosphatidylserine and Ca2+. Hydroxyapatite column chromatography showed only one peak of PKC activity with histone H1 and myelin basic protein as substrates. The enzyme was purified to near homogeneity by sequential chromatography on polylysine-agarose and phosphatidylserine affinity columns. The purified protein showed a molecular mass of 79 kDa on SDS/PAGE. The substrate specificity of the C. elegans enzyme was shown to be different from that of mammalian PKCs. Here we describe some of the properties of the nematode enzyme. (+info)
Synergistic activation of type III protein kinase C by cis-fatty acid and diacylglycerol.
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Micromolar concentrations of cis-fatty acid synergistically activate type III protein kinase C with diacylglycerol. This synergistic effect occurs at low concentrations of cis-fatty acid and diacylglycerol, and it is capable of inducing almost full activation of this protein kinase C subtype at a physiologically relevant Ca2+ concentration (2 microM). The synergistic activation mode can be observed even in the absence of Ca2+, but micromolar Ca2+ significantly enhances the type III protein kinase C activation. cis-Fatty acid also augments the diacylglycerol-induced activation of other subtypes (type I and II), although the effect is smaller than that observed in type III. Neither the diacylglycerol- nor the cis-fatty acid-dependent mode of activation can fully activate any of these subtypes at a physiological concentration of Ca2+ (2 microM). Our results suggest that the generation of three second messengers, i.e. the increase in intracellular Ca2+ concentration and the generation of both cis-fatty acid and diacylglycerol in the cell, may be necessary signals for protein kinase C activation, particularly for type III protein kinase C. (+info)
Salivary statherin. Dependence on sequence, charge, hydrogen bonding potency, and helical conformation for adsorption to hydroxyapatite and inhibition of mineralization.
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The structural domains of salivary statherin that are partly responsible for the protection and recalcification of tooth enamel were examined with respect to charge, sequence, hydrophobicity, hydrogen bonding potential, and conformation. Several fragments of statherin, 1-15 (SN15), 5-15 (SN11), 15-29 (SM15), 29-43 (SC15), 19-43 (SC25), and analogs of the N-terminal 15-residue sequence, where phosphoserines at positions 2 and 3 have been replaced by Ser (SNS15) and Asp (SNA15), respectively, were synthesized. The abilities of these fragments to adsorb at hydroxyapatite (HAP) surfaces and to inhibit its mineralization in supersaturated solutions were determined and compared with those of the whole statherin molecule, reported previously. The conformational preferences of the fragments both in aqueous and nonaqueous solutions were examined by circular dichroism. The highly charged N-terminal SN15 fragment has the greatest adsorption to HAP as compared with statherin and all other fragments. Its mineralization inhibitory activity is significantly greater than those of other fragments and comparable with that of the whole molecule. The dephosphorylated N-terminal fragment SNS15 shows a decreased tendency to adhere to and inhibit the formation of HAP, as compared with SN15. However, the substitution of Asp residues in place of phosphoserines (SNA15), restores the binding affinity and crystal growth inhibition properties, suggesting that the negative charge density at the N-terminal rather than any specific interaction of the phosphate group is important for HAP surface interactions. The C-terminal SC15 and SC25 fragments elicit a much higher affinity for HAP surface than that of the middle sequence (SM15), indicating that hydrogen bonding potential of the C-terminal sequence also contributes to the interaction of statherin with HAP. CD studies provide evidence that the N-terminal SN15 fragment has a strong tendency to adopt an ordered helical conformation, whereas the shorter N-terminal sequence, middle, and C-terminal fragments are structurally flexible and prefer to adopt scattered turn structures or unordered random conformations in organic and aqueous solutions. Collectively, the data indicate that the negative charge density, sequence (1-15), and helical conformation at the N-terminal region of statherin are important for its surface interaction with HAP. (+info)
Targeting deletion (homoeologous chromosome pairing locus) or addition line single copy sequences from cereal genomes.
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We describe here a protocol for obtaining clones containing sequences present in low copy-number from genomic DNA where moderately and highly repeated sequences predominate. Specific chromosomal regions can be targeted by using deletion or addition line material. We have used this protocol to identify a sequence which has been deleted in both the tetraploid and hexaploid wheat mutants for the homoeologous chromosome pairing locus. (+info)