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

Mutants resistant to 6-thioguanine were selected from CHO cells which were either temperature sensitive or proline requiring. These mutants were stable and had low levels of hypoxanthine guanine phosphoribosyl transferase (HGPRT). Hybrids were selected which were heteroallelic at the hgprt locus and complementation between the mutants used was not observed. Interallelic recombination at this locus would generate hgprt+ cells which could be selected in Littlefield's HAT medium. Selection experiments with hybrids containing three different pairs of mutants yielded no recombinants among populations of 4 x 106 - 2 x 107 cells. After treatment with the recombinagen mitomycin C, 3 putative recombinants were detected amongst 1.4 x 107 surviving cells from one hybrid. One of these strains was examined and shown to have a normal level of HGPRT and its heterozygosity at this locus was demonstrated by the segregation of colonies resistant to 6-thioguanine. It cannot be excluded that the rare hgprt+ colonies seen arose by mutation rather than by recombination. Mitotic allelic recombination therefore appears to be a much less frequent event in CHO cells than it is in lower eukaryotes. It is possible that mitotic recombination is effectively suppressed in mammalian cells to prevent the expression of deleterious recessive mutants.
Mol Gen Genet 1977 Nov 18
PMID:A search for allelic recombination in Chinese hamster cell hybrids. 60 Feb 66

Protein S5 and S12 were isolated from 30S ribosomal subunits of two E. coli mutants highly resistant to the antibiotic neamine, and of the parental strain. Proteinchemical analyses on these proteins led to the following results: a) In protein S5 the arginine residue in peptide T2 of the parental strain is replaced by glycine in one (nea 314) or serine in the other (nea 319) of the two mutants. b) In protein S12 The proline residue in peptide T15 of the parental strain is replaced by leucine in mutant nea 314 and by glutamine in mutant nea 319. Comparison of these results with those obtained in earlier studies on other mutants with altered ribosomal proteins revealed that the amino acid replacements in neamine resistant mutants and in "revertants" from streptomycin dependence occur at the same amino acid positions of proteins S5 and S12. Therefore it is likely that both types of mutants belong to the same class.
Mol Gen Genet 1975 Dec 23
PMID:Cooperative control of translational fidelity by ribosomal proteins in Escherichia coli. II. Localization of amino acid replacements in proteins S5 and S12 altered in double mutants resistant to neamine. 76 36

The proteolytic activity of the extracellular protease of Serratia marcescens was compared with that of trypsin on N, N-dimethyl casein. The peptides produced from exhaustive hydrolysis of alpha casein by the protease and by trypsin were of similar size as measured by gel filtration on P-10 Agarose. We conclude that the protease of S. marcescens in an endopeptidase with trypsin-like activity on proteins, producing oligopeptides. End group analysis of the peptides formed by the S. marcescens protease suggests that the protease has a unique substrate specificity, hydrolyzing only a peptide bond whose carboxyl group is donated by proline. The protease was inactive on the synthetic peptides with proline donating the carboxyl group, but hydrolyzed various types of natural proteins. Its narrow and novel substrate specificity makes this enzyme a potential tool for the determination of the primary structure of proteins.
Mol Cell Biochem 1976 Dec 10
PMID:The extracellular metalloprotease of Serratia marcescens. 2. Comparison with trypsin and substrate specificity. 79 98

A kinetic study of the influence of thyreotrope-releasing hormone (TRH) on prolactin turnover and synthesis by a new rat pituitary prolactin cell line (SD1) has been performed by means of pulse-chase experiments. After a 10-min [3H]leucine pulse, the chase was carried out in the presence or absence of TRH (54 nM), cycloheximide (3.6 X 10(-5)M) and/or [14C]-proline. The prolactin content of the cells in the medium was estimated using a radioimmunoassay technique. The specific radioactivity of prolactin in the medium was estimated after its isolation by disc gel electrophoresis. This kinetic study demonstrated, firstly, a rapid intracellular transit of newly synthesized prolactin (15 + 10 min or less); secondly, the existence of at least two intracellular prolactin pools; thirdly, a rapid effect of TRH on release of stored prolactin, which is independent of de novo protein synthesis, and fourthly, a delayed stimulating effect of TRH on prolactin synthesis.
Mol Cell Endocrinol 1975 Nov
PMID:Effect of thyreotrope-releasing hormone (TRH) on prolactin turnover in culture. 81 96

1. The characteristics of absorption of individual amino acids from amino acid mixtures simulating casein and from enzymic hydrolysates of casein containing oligopeptides as well as free amino acids are known to be different. The differences, which are attributable to mucosal uptake of small peptides, involve more rapid absorption from the enzymic hydrolysates of certain amino acids which are relatively slowly absorbed from the amino acid mixtures. This could lead to more effective utilization of amino acids from the enzymic hydrolysates than from the amino acid mixtures. 2. To obtain further information bearing on this hypothesis, we have used a recently developed technique for portal cannulation in the guinea pig to make a preliminary investigation of amino acid concentrations in the portal venous plasma at intervals after the infusion into the duodenum of equivalent amounts of (a) an amino acid mixture simulating casein and (b) a partial enzymic (papain followed by kidney peptidases) hydrolysate of casein, the two preparations being infused in separate experiments. 3. For some amino acids, such as leucine, isoleucine, valine, phenylalanine and lysine, the curves after the enzymic hydrolysate were fairly similar to the corresponding curves after the amino acid mixture, though usually slightly lower. With other amino acids, the curves after the enzymic hydrolysate were very much lower than the corresponding curves after the amino acid mixture. With serine, glutamine, proline and glycine this discrepancy was particularly great. 4. The results cannot yet be fully explained, but their main features are explicable by the hypothesis that the lower amino acid concentrations in portal plasma after the enzymic hydrolysate are the result of entry of amino acids into the portal blood in peptide form, in which they would not be detectable by the analytical technique employed, and possibly also of more rapid clearance of amino acids from the blood during absorption of this preparation.
Clin Sci Mol Med 1977 Mar
PMID:Amino acid concentrations in portal venous plasma during absorption from the small intestine of the guinea pig of an amino acid mixture simulating casein and a partial enzymic hydrolysate of casein. 84 57

Natural abundance carbon-13 and proton NMR spectra of bovine chromaffin granules have been obtained and analyzed using computer simulation techniques. High resolution spectra show the presence of a fluid aqueous phase containing epinephrine, ATP and a random coil protein. The protein spectrum contains unusually intense resonances due to glutamic acid and proline and has been simulated satisfactorily using the known amino acid composition of chromogranin A. The lipid phase of chromaffin granules gives rise to intense, but very broad, resonances in the carbon-13 spectrum. Protons in the lipid phase are also observable as a very rapid component of the proton-free induction decay (T2 approximately equal to 15 microns). Linewidths of the carbon-13 spectra have been used to set upper limits on rotational correlation times and on the motional anisotropy in the aqueous phase. These limits show that the aqueous phase is a simple solution (not a gel) that is isotropic over regions much larger than solute dimensions. No gel transition is observed between -3 and 25 degrees C. The carbon-13 spectra are definitely inconsistent with a lipoprotein matrix model and chromaffin granules previously proposed by Helle and Serck-Hanssen ((1975) Mol. Cell, Biochem. 6, 127-146). Relative carbon-13 intensities of ATP and epinephrine are not consistent with the known 1 : 4 mol ratio of these components. This fact suggests that epinephrine and ATP are not directly complexed in intact chromaffin granules.
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PMID:Analysis of the carbon-13 and proton NMR spectra of bovine chromaffin granules. 84 74

1. Plasma and buffy-coat vitamin C, urinary proline, hydroxyproline, creatinine and total amino acid concentrations were meausred in 23 healthy elderly subjects at intervals of 3 months. 2. There was a strong positive correlation between plasma vitamin C and buffy-coat vititamin C. 3. There were not significant correlations between plasma or buffy-coat vitamin CPAMIN C. 3. There were not significant correlations between plasma or buffy-coat vitamin C and total urinary hydroxyproline, whether expressed on a creatinine basis or on a total amino acid basis. Similarly, no significant correlations could be detected involving the proline/hydroxyproline ratio in urine hydrolysates. 4. There was a significant negative correlation between plasma or buffy-coat vitamin C and total urinary proline, when expressed per unit of total urinary proline, when expressed per unit of total urinary proline, when expressed per unit of total amino acids in the hydrolysates. This correlation was not observed with unhydrolysed urine, and it appeared to reside in the diffusible fraction, part of whose proline could be liberated by prolidase digestion. In addition, in the man, there was some evidence for a positive correlation between plasma or buffy-coat vitamin C and the ratio of total urinary amino acids to creatinine. 5. These results support the view that poor vitamin C status in elderly humans may be associated with a defect in collagen proline hydroxylation, reflected by increased excretion of proline-rich, collagen-derived peptides. If this interpretation is correct, it indicates a potential defect in connective tissue repair, and could form the basis of a functional test for subclinical vitamin C deficiency.
Clin Sci Mol Med 1977 May
PMID:Proline and hydroxyproline excretion and vitamin C status in elderly human subjects. 86 47

1. A jejunal perfusion technique has been used in normal volunteer subjects to study jejunal absorption of amino acid residues from a partial enzymic hydrolysate of casein in which about 50% of the amino acids existed as small peptides, and also from an equivalent mixture of free amino acids. 2. The effect of a high concentration of the dipeptide glycylglycine on the absorption of amino acid residues from these preparations was studied to quantify the importance of mucosal uptake of intact peptides during absorption of the partial hydrolysate of casein. 3. The results were unexpected. Glycylglycine significantly inhibited absorption of several amino acid residues (aspartic acid + asparagine, serine, glutamic acid + glutamine, proline, alanine, phenylalanine, threonine and isoleucine) from the free amino acid mixture, whereas it significantly inhibited the absorption of only two (serine, glutamin acid + glutamine) from the peptide-containing partial casein hydrolysate. 4. The effect of glycylglycine on absorption of amino acids from the mixture of free amino acids was apparently due to inhibition of amino acid uptake by free glycine liberated from the dipeptide during perfusion. The reason for the failure of glycylglycine to cause extensive inhibition of absorption from the partial hydrolysate is not clear. It may be due to glycylglycine being only a weak inhibitor of peptide uptake, but the possibility that some peptides are taken up by a system unavailable to glycylglycine has to be considered.
Clin Sci Mol Med 1977 Jul
PMID:Effect of glycylglycine on absorption from human jejunum of an amino acid mixture simulating casein and a partial enzymic hydrolysate of casein containing small peptides. 87 18

1. Absorption of [3H]glycine and [14C]-glycyl-L-proline at concentrations between 0-5 and 4 mmol/l was studied by perfusion in vivo of rat jejunal and ileal segments. Absorption was defined as net removal of radioisotope from the perfusate. Radioactivity assays and amino acid analyses were performed on perfusates and on mucosal tissue samples obtained from the perfused segments. 2. At the concentrations studied, absorption rates of glycine and glycylproline were proportional to concentration. Ileal rates were approximately 60% of jejunal rates. Glycylproline absorption was slightly faster than glycine absorption and was associated with the appearance in the perfusate of free glycine and proline in the ratio approximately 3:1. Intraluminal hydrolysis was insufficient to account for the amounts of free amino acids found and glycylproline hydrolase activity at the brush border is known to be minimal. 3. Glycylproline absorption apparently occurred by transport of the intact peptide followed by its intracellular hydrolysis. However, more than one-third of absorbed glycine and one-eighth of absorbed proline returned to the lumen as free amino acid. This reflux of glycine and proline was not proportional to their concentrations in the mucosa.
Clin Sci Mol Med 1977 Jun
PMID:Intestinal absorption of glycine and glycyl-L-proline in the rat. 88 32

The periodic protein collagen is of special interest for the study of the relationship which exists between the structure of a protein and that of its mRNA, because oligopeptides containing glycine, proline (hydroxyproline) and alanine occur with great frequency in it. Collagen is particularly rich in these amino acids, which have codons containing only G and/or C in the obligatory first and second positions. If unlimited choice of codons for all amino acids were to occur, the stretch of mRNA coding for an alpha-chain should contain about 40% G and 31% C (Bachra et al., 1974). These high values suggest that a considerable degree of secondary structure will occur, unless selective codon use would result in the avoidance of G and C in optional third codon positions. In the present paper putative secondary structure formation in collagen mRNA was studied. This was done by studying the positions and frequencies of hairpin structures which could contain stem sections composed of the coding triplets of the above mentioned amino acids and hairpin sections of 4-40 bases. Calculation of the free energy contributions of such hairpin structures, using published values for the contributions of base-pair stacking, hairpin, bulge and interior loops and also taking into account the possible minimum number of base-pairs required for helix nucleation from a single-strand RNA (3 adjacent AU-pairs or 1 or 2 adjacent GC-pairs) led to the following conclusions. A considerable number of alternative, mutually exclusive hairpins can be constructed.
J Mol Evol 1976 Aug 03
PMID:Self complementarity in messenger RNA of collagen. I. Possible hairpin structures in regions coding for oligopeptides of glycine, proline (hydroxyproline) and alanine. 96 90


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