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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Following the demonstration of peptidases in the rat hypothalamus which inactivate thyrotrophin-releasing hormone (TRH), a sensitive and specific radioimmunoassay for the releasing hormone was used to investigate the presence of similar peptidases in the rabbit hypothalamus. TRH was found to be rapidly inactivated by supernatant and particulate hypothalamic fractions, with higher peptidase activity in the supernatant than in the particulate fraction. An optimum pH of 7.3 within physiological limits was obtained for the enzymes in both the fractions examined. The results obtained confirm that the rabbit hypothalamus contains enzymes capable of inactivating TRH, and since it has been found that such peptidases interfere with studies on TRH biosynthesis, it is possible that the peptidases may play a part in controlling the releasing hormone's production. The specificity of the antiserum used in the radioimmunoassay has also suggested that the peptidases may cleave the C-terminal-ProNH2,-NH2 or both from the TRH molecule to cause inactivation.
Mol Cell Endocrinol 1976 Mar
PMID:Hypothalamic inactivation of thyrotrophin-releasing hormone. 0 45

1. A 25% faecal suspension in sodium chloride solution, incubated anaerobically at 37 degrees C for 48 h, showed excellent survival of all the main groups of faecal bacteria. 2. All faecal incubation systems studied generated large amounts of ammonia, particularly those in which bacterial counts fell during incubation. As normal faeces contain negligible amounts of urea this ammonia must have been generated from sources other than urea. 3. Ammonia was also generated by faeces delivered by sodium chloride enema, and by ileostomy fluid, indicating that the phenomenon is not confined to distal colonic contents. 4. Ammonia generation by incubated faeces was inhibited by prior autoclaving of the sample, but not by sterilization with gamma-irradiation. 5. Generation of ammonia by incubated stool was accompanied by release of large amounts of organic anion and a fall in pH. 6. These observations are interpreted as evidence that ammonia generated within the colon in situ is not derived exclusively from urea, but also from bacterial deamination of amino acids, peptides and proteins. Simultaneously bacterial activity generates large amounts of organacid. The presence of living bacteria is not essential for ammonia generation, provided that bacterial enzymes are present. 7. Bacterial generation of organic solute in faeces which have left the body is sufficiently rapid to cast serious doubts on the validity of faecal centrifugation, or other time-consuming techniques involving lengthy handling of faeces, as methods of obtaining extracellular faecal fluid for measurements of organic constituents or ammonia.
Clin Sci Mol Med 1976 Sep
PMID:Generation of ammonia from non-urea sources in a faecal incubation system. 0 21

The relative genetic position of the following four mutations of ribosomal protein S5 has been determined: spc-13, a mutation to spectinomycin resistance; stri N421 and strid1023, mutations suppressing dependence on streptomycin and sup0-1, a mutation suppressing partially the temperature-sensitive phenotype of an alanyl-tRNA synthetase mutation. The transduction experiments performed indicate that the spc-13 site is located in the S5 cistron proximal to the strA locus, that sup0-1 maps proximal to the aroE gene and that the striN421 and strid1023 loci are located between these two mutational sites. Proteinchemical analysis of the amino acid replacement in protein S5 of strain N421 (carrying the striN421 allele) has shown that an arginine residue is replaced by leucine which results in the appearance of a trypsin intensitive bond between the tryptic peptides T2 and T16. The same alteration has been previously found by Itoh and Wittmann (1973) in the S5 protein of strain d1023. Determination of the alteration of ribosomal protein S5 of strain 0-1 (sup0-1 allele) revealed that the C-terminal tryptic peptide is altered. It differs from that of the wild-type protein by the lack of five amino acids and the appearance of a C-terminal glycine residue instead of a lysine residue. This change can be explained by the deletion of eleven nucleotides in the S5 cistron of strain 0-1. The recent determination of the primary structure of ribosomal protein S5 (Wittmann-Liebold and Greuer, 1975) allows the ordering of the S5 alterations employed: The order is spc-13-strid1023 (striN421)-sup0-1 with the spc-13 amino acid replacement being located at the NH2-terminal portion of the S5 sequence and the alteration of strain 0-1 at the COOH-terminal end. The proteinchemical results are therefore in full agreement with the genetic data and unambiguously allow the conclusion that the S5 cistron is transcribed counterclock-wise on the Escherichia coli chromosome.
Mol Gen Genet 1975 Dec 30
PMID:Genetic position and amino acid replacements of several mutations in ribosomal protein S5 from Escherichia coli. 12 73

The interaction of nitrogenase with spin labels of four types have been studied. Conclusion about the presence of two SH-groups in the nitrogenase active site (one in Mo-Fe-protein and one in the Fe-protein) have been drawn from the correlation between the degree of inhibition of nitrogenfixing activity by the labels derived from p-Cl-Hg-benzoate and degree of binding of these labels to the nitrogenase molecule. Anaysis of EPR spectra of spin-labeled nitrogenase at 77 degrees K and at room temperature have shown that the labels bind to the free SH-groups and interact with iron containing center (ICC) of nitrogenase through the exchange mechanism. Distance between SH-group and ICC have been found to be 12 A. Spin labels derived from isocyanide have been bound directly to ICC in amount of 6--10 labels per one nitrogenase molecule. Due to the exchange interaction between these labels they give the singlet ESR spectra both at 77 degrees and at room temperature which is characteristic for the closely disposed labels. From this fact a conclusion have been drawn about the cluster structure of ICC. The labels derived from iodoacetamide ana maleimide bind SH- and NH2-groups of nitrogenase molecules. Analysis of temperature dependence of the effective rotational frequency of this labels have revealed a conformational transition in nitrogenase molecule at 19 degrees C, that has made it possible to explain the break in the Arrenius plots of enzyme activity.
Mol Biol (Mosk)
PMID:[Study of the nitrogenase from Azotobacter vinelandii by the method of spin labels]. 17 70

The surface of liposomes and natural membranes has been studied by the method of "spin label--spin probe". Various nitroxyl radicals have been attached to membranes either dueto covalent binding with NH2-groups of phosphatidylethanolamine or due to hydrophobic interactions. Addition of paramagnetics of different charge signs (potassium ferricyanide and dibenzenechromium iodide) to spin labeled membranes results in a decrease of the EPR line intensity without marked broadening. Since the paramagnetic is attached to the membrane surface near the label it broadens the label's EPR spectrum so that it can not be observed. In this case one can observe only the spectrum of labels which have no paramagnetics in the vicinity, the nitroxyl part of radicals being inaccessible to direct paramagnetic impacts. The constants of binding of paramagnetics to the membrane surface have been determined from these experiments. All results (including the assymetry of label rotation) can be explained most simply by assuming that the polar lipid groups are oriented parallel to the membranes surface.
Mol Biol (Mosk)
PMID:[Spin label study of the surface of lipid bilayers]. 20 76

Inhibition of plasma prolactin levels by 2-bromo-alpha-ergocryptine (CB-154) caused a 60% decrease and potentiated the inhibitory effects of [D-Ala6,des-Gly-NH2(10)]LHRH ethylamide on testicular LH receptor levels. Animals treated with the LHRH agonist showed reduced plasma and testicular testosterone levels and elevated progesterone concentration. This progesterone rise was further increased in animals having high circulating prolactin levels but was prevented by CB-154. These data demonstrate that: (1) treatment with the LHRH agonist induces a blockage in the steroidogenic pathway at a step between progesterone and testosterone and (2) prolactin levels to an apparent accentuation of this blockage reflected by higher progesterone levels.
Mol Cell Endocrinol 1979 Jan
PMID:Down-regulation of testicular androgen biosynthesis and LH receptor levels by an LHRH agonist: role of prolactin. 22 Dec 86

1. Ammonia and urea transport across the colonic mucosa was studied by a perfusion technique in four subjects with colonic exclusion for chronic hepatic encephalopathy. 2. Reduction of luminal pH inhibited net and unidirectional transport of ammonia from lumen to plasma, but net absorption from high luminal concentrations persisted at low pH. 3. Neither addition of urea to the perfusate nor intravenous infusion of urea produced a consistent increase in the colonic excretion of ammonia when ammonia-free solutions were perfused. 4. In one subject intravenous infusion of (15N)-ammonium chloride produced rapid labelling of colonic effluent ammonia and within 60 min the specific enrichments of ammonia in effluent and in arterial plasma were approximately equal. 5. During perfusion of nitrogen-free solutions, only small amounts of urea appeared in the effluent, suggesing limited permeability of the colonic mucosa to urea. 6. These results are discussed in relation to the equilibration of ammonia across the colonic mucosa by both ionic and non-ionic diffusion. The lack of evidence of 'juxtamucosal' (as opposed to luminal) ureolysis is in contrast to other observations on the intact colon. The possible reasons for and implications of this discrepancy are discussed.
Clin Sci Mol Med 1975 Apr
PMID:Ammonia and urea transport by the excluded human colon. 23 10

A modified procedure for the purification of E. coli galactose-1-phosphate uridyl transferase (E.C. 2.7.6.12) was developed which reproducibly gives pure enzyme. The purified enzyme was shown to be a dimeric protein with a subunit molecular weight of 41,000 and its amino acid composition and content of free sulfhydryl groups were determined. The N-terminal and C-terminal amino acid sequences were found to be NH2-thr-gln-phe-asn-pro-val-asp and -ser(val leu)-ala-COOH respectively. This N-terminal sequence allowed the identification of the start of the transferase gene in the DNA sequence determined by GRINDLEY. Furthermore it appears to define a nine base intercistronic region between the epimerase and transferase genes.
Mol Cell Biochem 1979 Feb 09
PMID:E. coli galactose-1-phosphate uridyl transferase: N-terminal and C-terminal sequences. 38 9

The current status of the purification and characterization of human angiotensinogen is reviewed. One problem encountered in the past has been the copurification of a protein with similar porperties. This protein has tentatively been designated alanine-protein. An efficient separation of angiotensinogen and alanine-protein was obtained on a zinc chelate column. Alanine-protein has been purified and its amino acid and carbohydrate composition determined. The COOH-terminal amino acid and the NH2-terminal amino acid were determined to be serine and alanine, respectively. Alanine-protein exhibited multiple forms on isoelectric focusing.
Mol Cell Biochem 1979 Sep 28
PMID:Human plasma angiotensinogen: a review of purification procedures. 39 Mar 63

Two sheep with a ruminal fistula and an isolated small rumen were studied for the secretion of ammonia nitrogen, urea nitrogen, and amino nitrogen into the isolated rumen at different levels of volatile fatty acids (VFA) (50, 133-97, and 97-66 M Mol 1(-1)) in the rumen. The VFA level in the rumen was found to exert a great influence on the quantitative secretion of endogenous nitrogen from the blood through the rumen wall into rumen content. When the VFA level in the rumen was increased by administration of a single dose of acetic, propionic, and butyric acid, the secretion of ammonia nitrogen and amino nitrogen abruptly dropped and the secretion of urea into the isolated rumen slightly increased. The over-all amount of nitrogen (NH3-N + urea-N + amino-N) that had passed into the isolated rumen in the course of an hour showed a highly significant correlation with the passage of nitrogen in the form of ammonia and amino nitrogen and was greatest before the application of VFA to the rumen, i.e. at the level of 50 m mol 1-1. Of the metabolites under study, which were passing to the isolated rumen, amino nitrogen shared the greatest proportion (45.38-46.54%). When the VFA level in the rumen was raised, the proportion of ammonia secreted to the isolated rumen decreased and the proportion of urea in the total amount of nitrogen increased.
 ...
PMID:[Relationship between the volatile fatty acids (VFA) in the rumen and nitrogen secretion into isolated sheep's rumen]. 41 43


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