Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:1.1.1.3 (HSD)
3,464 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Specific activity of 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) was measured in 48 tissue specimens of human female breast cancer and, in addition, 48 nonmalignant tissue specimens obtained in each case from the same cancer-bearing breast. In all cases the nonmalignant tissue showed greater conversion of estradiol-17 beta into estrone than the neoplastic tissues. In normal human breast tissue of premenopausal women specific enzyme activity depended on the phase of the MENSTRUAL CYCLE: the highest values of 17 beta-HSD activity were found in the early secretory phase. To determine the intracellular distribution of the 17 beta-HSD, purified microsomes, mitochondria, peroxysomes, lysosomes, nuclei and cytosol fractions were prepared. The purity of each fraction was monitored by marker enzymes. It was found that the 17 beta-HSD was mainly located in mitochondria and microsomes. Furthermore it could be demonstrated that the microsomal enzyme was bound tightly to the membranes of the endoplasmic reticulum, while the mitochondrial 17 beta-HSD was mainly associated with the outer membranes of the organelle. Kinetic parameters (Km-values, coenzyme requirements and maximal velocities) of a cytoplasmic, nuclear, mitochondrial and microsomal 17 beta-HSD of normal and neoplastic human mammary tissue were compared. Maximal velocity was highest in enzyme preparations of normal mammary tissue obtained from premenopausal women in the early secretory phase. Km-values wrere nearly identical in normal and neoplastic mammary tissue preparations (approx. 1 X 10(-6) M). NAD was more efficient than NADP as a cofactor. For the conversion of estradiol to estrone the optimum temperature was approximately 40 degrees C and the optimum pH 9.5. For the reduction of estrone the optimum pH was 6.5. Sulphydryl groups were shown to be essential for catalysis.
...
PMID:Comparison of the in vitro conversion of estradiol-17 beta to estrone of normal and neoplastic human breast tissue. 1 41

Through the use of specific immunoadsorbent columns, it is shown that Escherichia coli aspartokinase I-homoserine dehydrogenase I, aspartokinase II-homoserine dehydrogenase II, aspartokinase III, and homoserine kinase, enzymes involved in the same complex biosynthetic pathway, share antigenic determinants. This raises the question of a common origin for the four cibtenoirart kinases. (Aspartate kinase or ATP:L aspartate 4-phosphotransferase, EC 2.7.2.4; homoserine dehydrogenase or Lhomoserine:NADP oxidoreductase, EC 1.1.1.3; homoserine kinase or ATP:L-homoserine O-phosphotransferase, EC 2.7.1.39.)
...
PMID:Evolution of biosynthetic pathways: immunological approach. 4 55

The regulation of aspartokinase and homoserine dehydrogenase has been studied in three Acetobacter and two Gluconobacter species. Both enzymes were regulated by feedback inhibition. Aspartokinase was inhibited by L-threonine and concertedly inhibited by L-threonine plus L-lysine. The homoserine dehydrogenase was NADP-specific and was inhibited by L-threonine. Separation of the two enzymes by ammonium sulphate fractionation was possible in Acetobacter peroxydans, A. rancens and Gluconobacter melanogenus but not in A. liquefaciens or G. oxydans.
...
PMID:Regulation of aspartokinase and homoserine dehydrogenase in acetic acid bacteria. 16 8

Six enzymes involved in the conversion of aspartate to threonine have been extracted from Escherichia coli and separated from each other. Two of these enzymes, aspartokinase and homoserine dehydrogenase, have also been partially purified from Rhodopseudomonas spheroides. In an attempt to determine whether small changes in the kinetic properties of individual enzymes are important to the regulation of metabolic flux through a coupled reaction system, the partially purified enzymes were recombined in a variety of ways under reaction conditions designed to resemble the in vivo situation. These conditions include: use of an entire metabolic system rather than a single reaction; high enzyme concentrations at the same relative concentrations as found in the cell; and low, steady-state concentrations of substrates and products. Metabolic flux was followed spectrophotometrically and the concentrations of aspartic semialdehyde, hemoserine, O-phosphohomoserine, and threonine were measured. The results indicate that the threonine concentration is of major importance in regulating metabolic flux by inhibiting aspartokinase, the first reaction in threonine in the pathway. When threonine-insensitive aspartokinases were used, concentrations reached higher levels and the rate of NADPH oxidation remained higher. The fact that neither aspartic semialdehyde nor homoserine accumulated as the threonine concentration increased and the lack of correlation between changes in metabolic flux and ADP/ATP or NADPH/NADP ratios indicate that more subtle forms of metabolic regulation, such as "reverse cascade", secondary feedback sites, or "energy charge", are of little regulatory importance in this isolated, metabolic system. The results also emphasize the need for caution in projecting in vivo control mechanisms from in vitro experiments.
...
PMID:Regulation of a metabolic system in vitro: synthesis of threonine from aspartic acid. 17 64

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.
...
PMID:Methionine-repressible homoserine dehydrogenase of Serratia marcescens: purification and properties. 18 74

Detailed enzyme kinetic parameters of the reactions catalyzed by the two 17beta-hydroxysteroid dehydrogenases (17beta-HSD), which were solubilized from the microsomes of human placenta by treatment with phospholipase A, followed by enrichment and separation were determined. Both enzymes are strictly substrate specific. The most active substrate of one of the 17beta-HSD (fraction A) is estradiol-17beta, the other 17beta-HSD (fraction B) is sensitive to testosterone. Both NAD and NADP can serve as hydrogen transferring coenzymes, the latter giving about one-third of the initial rate of the former. With respect to the influence of temperature, different buffers and pH values, Michaelis constants (Km) with estradiol-17beta and testosterone as substrates, the solubilized and separated microsomal 17beta-HSD behave like those isolated from the cytoplasmic fraction. The two 17beta-HSD, after solubilization from the microsomal fraction of human placenta, enrichment and separation from each other, show only a little activity for the transfer of hydrogen between C17 of estradiol-17beta and C17 of androstenedione. On the other hand, intact microsomes and an integrated system prepared by recombination of the 17beta-enzymes by preincubation in phosphate buffer are able to catalyse very actively the transfer of hydrogen between estradiol-17beta and androstenedione. The effect of temperature and time on the recombination of the two enriched and separated microsomal enzyme activities and the determination of the pH-optimum of the hydrogen transfer reaction are described. Finally it is proposed that the hydrogen transfer between steroid hormones represents an aspect of the true reaction mechanism of steroid hormones: Steroid hormones function as hydrogen transferring coenzymes by forming part of a chain of hydrogen carriers.
...
PMID:[Microsome-associated 17beta-hydroxysteroid dehydrogenases of human placenta, ii kinetic studies and characterization of the solubilized estradiol-and testosterone-"sensitive" 17beta-HSD-Activities]. 23 76

Microsomal 17 beta-hydroxysteroid dehydrogenase obtained from the human secretory endometrium (17 beta-HSD) was solubilized with triton X-100. A 4-fold purification was achieved by ammonium sulphate precipitation and isoelectric focusing. In the presence of glycerol the partially purified enzyme was stable at 4 degrees C for at least 48 h. Using crude microsomes, the conversion of oestradiol to oestrone was linear with time and with the concentration of protein. The optimum temperature was approximately 40 degrees C and the optimum pH 9.4. For the reduction of oestrone the optimum pH was 6.5. With NAD, oestradiol was oxidized approximately three times more rapidly than with NADP. Km-values for oestradiol were nearly the same in endometrial carcinoma and in proliferative and secretory endometrium (i.e. approximately 3 X 10(-6) M). The maximal velocity was highest in secretory endometrium. Testosterone and androstenedione could also serve as substrates but they were interconverted more slowly than oestradiol and oestrone. Sulphhydryl groups were shown to be essential for catalysis.
...
PMID:Studies on 17 beta-hydroxysteroid dehydrogenase in human endometrium and endometrial carcinoma. III. Partial purification and characterization of the microsomal enzyme. 24 Nov 86

The growth of Clostridium group P strain C48-50 [an anaerobe that contains 12alpha-hydroxysteroid dehydrogenase (12alpha-HSDH) in the absence of other dehydrogenases active upon bile salts] is greatly enhanced by the addition of 2.0% d-fructose or d-glucose to the growth medium. Other sugars were less effective. The production of NADP-dependent 12alpha-HSDH paralleled the growth of the organism which was optimal at 72 hr. Growth (and enzyme production) were suppressed by the addition of bile salt to the medium; the order of suppression was deoxycholate > chenodeoxycholate >> cholate; 1 mM of either of the dihydroxy-bile salts inhibited 96% of the growth and 100% of the enzyme production. Kinetic studies on cell-free preparations of 12alpha-HSDH revealed a pH optimum of 7.8 with greater linearity of NADP evolution with time occurring only at more alkaline pH values (9-10). Lineweaver-Burke plots revealed Michaelis constant (K(m)) values in the range of 3-5 x 10(-4) M for deoxycholate and its glycine and taurine conjugates, while higher values were found for cholate and conjugates (K(m) value for taurocholate was 3 x 10(-3) M). Although there was no activity with NAD, 12alpha-HSDH was shown to bind onto both NAD- and NADP-Sepharose columns, with stronger binding on the latter. The enzyme was purified 20-fold by NAD-Sepharose chromatography. The molecular weight was estimated at 100,000 by Sephadex G-200 and a series of molecular weight markers. Substrate specificity studies showed that a variety of bile salts containing 12alpha-OH groups reacted; notably, the 3alpha-sulfates of cholate and deoxycholate were nonsubstrates.-Macdonald, I. A., J. F. Jellett and D. E. Mahony. 12alpha-Hydroxysteroid dehydrogenase from Clostridium Group P strain C48-50 #29733: partial purification and characterization.
...
PMID:12alpha-Hydroxysteroid dehydrogenase from Clostridium group P strain C48-50 ATCC No. 29733: partial purification and characterization. 43 63

A morphological and histochemical study has been made of ovarian surface epithelium during the sexual cycle of seasonally breeding birds: crow (Corvus splendens) and common myna (Acridotheres tristis). The surface epithelium is composed of a single layer of compactly arranged columnar and flat cells in the quiescent ovary. It develops numerous villi during the breeding season. The formation of villi has been correlated with the proliferation of cells which are subsequently incorporated into the ovarian stroma where they appear to form follicle and thecal cells around the growing oocytes as evidenced by the close similarities in the morphological and histochemical characteristics of these cell types. As the ovarian activity increases, the surface epithelial cells show increasing amounts of RNA and proteins, which are indicative of their rapid multiplication. No lipids and enzyme activities of acid and alkaline phosphatases, ATPase. DPN- and TPN- diaphorases and delta5-3beta HSDH have been detected in the surface epithelium of both quiescent and active ovaries.
...
PMID:Morphological and histochemical observations on the ovarian surface epithelium during the reproductive cycle of crow (Corvus splendens) and myna (Acridotheres tristis). 45 56

A morphological and histochemical study has been made of the primordial and early growing oocytes in the ovaries of crow (Corvus splendens) and common myna (Acridotheres tristis). The primordial oocytes in the myna ovary are loosely arranged in groups or nests, whereas in crow they form compact nests surrounded by highly vascularized connective tissue bands or lie in layers beneath the surface epithelium. The primordial oocytes in both the species are surrounded by flat granulosa cells whose number, shape, and cytochemical properties change with the initiation of growth. The oocyte nucleus shows a single basophilic nucleolus and thick diplotene chromosomes. With the initiation of growth, the number of nucleoli increases; simultaneously the chromosomes attain lampbrush configuration. Crescent-shaped Balbiani's vitelline body consists of ribonucleoproteins, lipoproteins, and phospholipids. The amount of these substances increases with the oocyte growth. The nature of proteins and lipids in the ooplasm and follicular epithelium also changes with the oocyte growth. Some randomly distributed protein bodies are also present in the ooplasm of primordial follicles. They disappear with the initiation of oocyte growth. The enzyme activities of acid phosphatase, NADP-diaphorase and NAD-diaphorase, also increase in the Balbiani's vitelline body with the oocyte growth. Alkaline phosphatase and delta 5-3 beta-HSDH activities are not seen. The possible functional significance of these morphological and histochemical changes has been discussed in relation to the initiation of growth in quiescent oocytes.
...
PMID:Morphological and histochemical observations on the primordial and early growing oocytes of crow (Corvus splendens) and myna (Acridotheres tristis). 47 89


1 2 3 4 5 6 7 8 9 10 Next >>

---