Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.1.1.3 (HSD)
 3,464 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In Escherichia coli K12 the biosynthetic pathway of lysine, methionine and threonine is characterized by three isofunctional aspartokinases and two homoserine dehydrogenases. A single polypeptide chain carries the threonine-sensitive aspartokinase and homoserine dehydrogenase (AK I-HDH I), and a different polypeptide chain carries the methionine-repressible aspartokinase and homoserine dehydrogenase (AK II-HDH II). Immuno-adsorbants prepared with rabbit antibodies against AK I-HDH I bind the lysine-sensitive aspartokinase (AK III), the AK II-HDH II, and the homoserine kinase (HSK), an enzyme of the threonine biosynthetic pathway. Saturation of the immunoadsorbant with AK I-HDH I results in a decreased binding capacity for the other enzymes. Displacement of bound AK III or HSK can be obtained with pure AK I-HDH I, showing that the affinity of the antibodies to homologous antigens is higher than to heterologous ones. Immunoadsorbants prepared with anti-HSK antibodies show the same type of recognition: binding of the three aspartkinases and a capacity to displace the heterologous antigens bound. Accordingly, the same antibodies, implicated in the binding of the homologous antigen, bind the other enzymes. None of the other enzymes of the pathway, or the other kinases tested are recognized by the two immunoadsorbants. It can be postulated that in E. coli K12, duplication of a common ancestor gene gave rise to the three aspartokinases and to the homoserine kinase; two of the genes coding for the aspartokinases fused with those coding for the homoserine dehydrogenases. Indicating that only few epitopes are shared by these enzymes, by conventional immuno-diffusion techniques no precipitation lines appeared with antibodies against AK I-HDH I and the other proteins.
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PMID:Immunological cross reactivity of four enzymes involved in the biosynthetic pathway of lysine, methionine and threonine in Escherichia coli K12. 6 12

Serratia marcescens Sa-3 possesses two homoserine dehydrogenases and neither has any aspartokinase activity unlike the case of Escherichia coli enzymes. The two enzymes have been separated. One of them is active with either NAD+ or NADP+ and has been purified about 180-fold to homogeneity. This enzyme is completely repressed by the presence of 1 mM methionine or homoserine in the growth medium, but its activity is unaffected by any amino acid of the aspartate family either singly or together. In many of its properties (such as pH optimum, Km for substrate and cofactors), it resembles its counterpart in E. coli K12. Potassium ions stabilize the enzyme but are not essential for activity. Its molecular weight is around 155,000 as determined by gel filtration and approximately 76,000 by SDS-polyacrylamide gel electrophoresis. This suggests that the enzyme has two subunits (polypeptide chains) in the molecule: 8 M urea has no effect on enzyme activity. This enzyme represents approximately 30% of the total homoserine dehydrogenase activity of S. marcescens unlike in Salmonella typhimurium and E. coli K12 where it is a minor or a negligible component.
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PMID:Methionine-repressible homoserine dehydrogenase of Serratia marcescens: purification and properties. 18 74

The dimeric bifunctional enzyme aspartokinase II-homoserine dehydrogenase II (Mr = 2 X 88,000) of Escherichia coli K12 can be cleaved into two nonoverlapping fragments by limited proteolysis with subtilisin. These two fragments can be separated under nondenaturing conditions as dimeric species, which indicates that each fragment has retained some of the association areas involved in the conformation of the native protein. The smaller fragment (Mr = 2 X 24,000) is devoid of aspartokinase and homoserine dehydrogenase activity. The larger fragment (Mr = 2 X 37,000) is endowed with full homoserine dehydrogenase activity. These results show that the polypeptide chains of the native enzyme are organized in two different domains, that both domains participate in building up the native dimeric structure, and that one of these domains only is responsible for homoserine dehydrogenase activity. A model of aspartokinase II-homoserine dehydrogenase II is proposed, which accounts for the present results.
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PMID:Proteolysis of the bifunctional methionine-repressible aspartokinase II-homoserine dehydrogenase II of Escherichia coli K12. Production of an active homoserine dehydrogenase fragment. 33 67

A library of EcoRI DNA fragments from Brevibacterium flavum was constructed using plasmid vector. The genes complementing ThrA2 and ThrB mutations in Escherichia coli were identified in the library. The gene thrA2 of B. flavum codes for mutant enzyme homoserine dehydrogenase insensitive to inhibition by threonine. The genes thrA2 and thrB are localized wihtin the EcoRI fragment 4.1 kb long and are expressed under the control of their own promoters in E. coli cells. Structural and functional analysis of cloned C. glutamicum gene ilvA was performed. The gene of C. glutamicum complemented ilvA mutation in E. coli and appeared to be localized within the EcoRI--SacI DNA fragment 1.6 kb in size. Using E. coli minicells we have demonstrated that the gene ilvA of C. glutamicum controls the synthesis of polypeptide of relative molecular mass 50 kD.
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PMID:[Cloning and structural-functional analysis in Escherichia coli of genes of glutamate-producing corynebacteria controlling biosynthesis of amino acids of aspartic acid series]. 219 95

cDNA clones for 17 beta-hydroxysteroid dehydrogenase (17-HSD; EC 1.1.1.62) were isolated from a placental lambda gt11 expression library using polyclonal antibodies against placental 17-HSD. The largest cDNA contained 1325 nucleotides, consisting of a short 5'-noncoding segment, a coding segment of 987 nucleotides terminated by a TAA codon, and a 329 nucleotide long 3'-noncoding segment. The open reading frame encoded a polypeptide of 327 amino acid residues with a predicted Mr of 34853. The amino acid sequence of 23 N-terminal amino acids determined from purified 17-HSD agreed with the sequence deduced from cDNA. The deduced amino acid sequence also contained two peptides previously characterized from the proposed catalytic area of placental 17-HSD.
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PMID:Complete amino acid sequence of human placental 17 beta-hydroxysteroid dehydrogenase deduced from cDNA. 284 51

The entire threonine operon (thrA(1)5A(2)5BC) of Serratia marcescens TLr156, which lacks threonine-mediated feedback inhibition of both aspartokinase I (AK I) and homoserine dehydrogenase I (HD I), was cloned on a multicopy plasmid pLG339. Hybrid plasmid pSK301 carried a 6.5-kb chromosomal DNA. Several derivatives of pSK301 with Tn1000 insertions were obtained. By examining the phenotypes and the physical maps of these plasmids, we could define the loci of the thrA(1)5A(2)5, thrB, and thrC genes. The thrA(1)5A(2)5 and thrC gene products were identified by the maxicell method as proteins with Mrs of 85,000 and 43,000, respectively. The thrA(1)5A(2)5 genes encode a single polypeptide similar to the thrA1A2 genes of Escherichia coli. Plasmid pSK301 was introduced into S. marcescens T-1112, in which both AK I and HD I are produced constitutively. The resulting transformant carried five to six copies of pSK301 per chromosome and produced the AK I and HD I enzymes at three to four times higher level than control strain T-1112[pLG339]. Strain T-1112[pSK301] produced four times higher levels of threonine than strain T-1112[pLG339], yielding about 35 mg of threonine per ml of a medium containing sucrose and urea.
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PMID:Cloning and characterization of the mutated threonine operon (thrA(1)5A(2)5BC) of Serratia marcescens. 312 45

The Bacillus subtilis hom gene, encoding homoserine dehydrogenase (L-homoserine:NADP+ oxidoreductase, EC 1.1.1.3) has been cloned and its nucleotide sequence determined. The B. subtilis enzyme expressed in Escherichia coli is sensitive by inhibition by threonine and allows complementation of a strain lacking homoserine dehydrogenases I and II. Nucleotide sequence analysis indicates that the hom stop codon overlaps the start codon of thrC (threonine synthase) suggesting that these genes, as well as thrB (homoserine kinase) located downstream from thrC, belong to the same transcription unit. The deduced amino acid sequence of the B. subtilis homoserine dehydrogenase shows extensive similarity with the C-terminal part of E. coli aspartokinases-homoserine dehydrogenases I and II; this similarity starts at the exact point where the similarity between E. coli or B. subtilis aspartokinases and E. coli aspartokinases-homoserine dehydrogenases stops. These data suggest that the E. coli bifunctional polypeptide could have resulted from the direct fusion of ancestral aspartokinase and homoserine dehydrogenase. The B. subtilis homoserine dehydrogenase has a C-terminal extension of about 100 residues (relative to the E. coli enzymes) that could be involved in the regulation of the enzyme activity.
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PMID:Cloning and nucleotide sequence of the Bacillus subtilis hom gene coding for homoserine dehydrogenase. Structural and evolutionary relationships with Escherichia coli aspartokinases-homoserine dehydrogenases I and II. 313 60

We have previously shown that a stroma-associated paracrine influence may occur in the human breast. In particular, human breast fibroblasts secrete a factor which stimulates reductive 17 beta-oestradiol dehydrogenase (HSD) activity, thereby regulating tissue concentrations of 17 beta-oestradiol. We report here the results of experiments designed to establish the nature of the enzyme activity stimulating factor. In vitro cell culture techniques were used, in which human breast fibroblast-conditioned medium was used to grow the human breast cancer cell line, MCF-7, for 6 days, after which the reductive HSD activity of the monolayers was assessed. The fibroblastic reductive HSD stimulating factor was found to be a trypsin-sensitive polypeptide. The polypeptide eluted from a Sephadex G-75 column as a peak corresponding to a molecular weight of about 50 kDa. The polypeptide exerts its effects by altering the Vmax of 2 of the cytosolic forms of HSD within MCF-7 cells. This is achieved by a protein-synthesis-dependent but calmodulin-independent mechanism. These results provide further evidence of a paracrine effect by stromal tissue within the human breast and have important implications with respect to the aetiology and treatment of breast cancer.
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PMID:Paracrine influence of human breast stromal fibroblasts on breast epithelial cells: secretion of a polypeptide which stimulates reductive 17 beta-oestradiol dehydrogenase activity. 316 8

The renaturation of aspartokinase-homoserine dehydrogenase and of some of its smaller fragments has been investigated after complete unfolding by 6 M guanidine hydrochloride. Fluorescence measurements show that a major folding reaction occurs rapidly (in less than a few seconds) after the protein has been transferred to native conditions and results in the shielding of the tryptophan residues from the aqueous solvent; this step also takes place in the fragments and probably corresponds to the independent folding of different segments along the polypeptide chain. The reappearance of the kinase activity, which is an index of the formation of "native" structure within a single chain, is much slower (a few minutes) and has the following properties: it is involved in a kinetic competition with the formation of aggregates; it has an activation energy of 22 +/- 5 kcal/mol; it is not related to a slow reaction in unfolding and thus probably not controlled by the cis-trans isomerization of X-Pro peptide bonds; its rate is inversely proportional to the solvent viscosity. It seems as if this reaction is limited by the mutual arrangement of the regions that have folded rapidly and independently. It is proposed that the mechanism where a fast folding of domains is followed by a slow pairing of folded domains could be generalized to other long chains composed of several domains; such a slow pairing of folded domains would correspond to a rate-limiting process specific to the renaturation of large proteins. The reappearance of the dehydrogenase activity measures the formation of a dimeric species. The dimerization can occur only after each chain has reached its "native" conformation.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Mechanism of renaturation of a large protein, aspartokinase-homoserine dehydrogenase. 360 93

20 alpha-Hydroxysteroid dehydrogenase (20 alpha-HSD) from bull testis has been purified to homogeneity and characterized in terms of apparent molecular weight, lack of subunit composition, substrate and cofactor specificity and certain kinetic parameters. The enzyme activity is localized in the 105,000 g supernatant and is stable at 4 degrees C in the presence of glycerol and dithiothreitol. Purification was achieved by ammonium sulfate precipitation followed by affinity chromatography on reactive red 120-agarose and subsequent gel filtration. The apparent molecular weight of the homogeneous enzyme, as determined by gel filtration on Sephacryl S-300 is 34,000. The mobility of the enzyme in sodium dodecyl sulfate (SDS) gel electrophoresis corresponds to a mol. wt of 40,000. These observations indicate that the enzyme is a single-stranded, monomeric polypeptide. The enzyme catalyzes the reduction of the 17-hydroxyprogesterone to 17,20 alpha-dihydroxy-4-pregnene-3-one in the presence of NADPH, the preferred cofactor. Homogeneous 20 alpha-HSD has an SA of 115 mIU/mg, and has been purified 14,000-fold with an overall 68% recovery. It exhibits a pH optimum at 5.6 and appears to be highly specific for 17-hydroxyprogesterone with an apparent Km-value of 7.3 X 10(-5) M. Androstenedione and corticosterone do not serve as substrates under the described experimental conditions. The enzyme does not possess 17 alpha- or 17 beta-HSD activity.
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PMID:Purification and characterization of 20 alpha-hydroxysteroid dehydrogenase from bull testis. 386 9


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