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Biomedical subjects

C Prasad

Publications and source records attributed to C Prasad.

At least 163 records · Page 9Linked to original sources
PubMed1980

The subcellular and organ distribution and natural form of histidyl-proline diketopiperazine in rat brain determined by a specific radioimmunoassay.

Histidyl-proline diketopiperazine is produced in brain as a product of the metabolism of thyrotropin-releasing hormone. A number of the previously observed central nervous system and pituitary activities resulting from an exposure to thyrotropin-releasing hormone appear to involve the conversion of the releasing factor to the cyclic dipeptide. In the present study, the development of a rabbit antiserum that is highly specific for histidyl-proline diketopiperazine is described; the antiserum has essentially no capability to bind thyrotropin-releasing hormone or a number of other related peptides. The antibody can also distinguish between the natural form of the cyclic dipeptide and a diastereomer containing D-proline. A procedure for extraction, with high yield, of histidyl-proline diketopiperazine from brain is described. With the aid of the specific antiserum it was found that the preponderance of the cyclic dipeptide in rat brain is bound to high molecular weight material, mainly in the range of Mr = 70,000; histidyl-proline diketopiperazine can be disassociated from this material by boiling in salt/methanol solution. The concentration of the dipeptide in rat brain is in the range of 275 to 565 pmol/brain, approximately 2.5 times the concentrations determined for thyrotropin-releasing hormone (113 to 210 pmol/brain). A study of the subcellular distribution of histidyl-proline diketopiperazine and thyrotropin-releasing hormone suggests that the releasing factor is concentrated in synaptosomal vesicles while the diketopiperazine is not. A determination of the regional distribution of thyrotropin-releasing hormone and histidyl-proline diketopiperazine indicated that both peptides are found in highest concentrations in pituitary and hypothalamus, but are detectable in other areas of brain as well.

Animals↗
PubMed1980

Effect of wheat and Bengalgram diets on brain glutamate metabolism in postweanling rats.

Six groups of five female rats each aged 6 weeks at start were fed different diets for a period of 15 days. The protein sources of diets used were: a) 10% casein: b) wheat: c) Bengalgram: d) wheat + lysine: and e) Bengalgram + methionine + cystine + tryptophan, all containing 1.6 g nitrogen/100 g, and f) 20% casein (3.2 g nitrogen/100 g diet). The group of five rats fed a 10% casein diet served as control. It was observed that total brain RNA, protein and free alpha amino nitrogen content and protein/DNA ratio were significantly decreased on wheat and Bengalgram diets as compared to the control. The specific activities of glutamine synthetase, glutaminase I, glutaminase II and glutamate decarboxylase and concentrations of aspartic acid, glutamic acid, glutamine and gamma-aminobutyric acid (GABA) in the brain were also decreased on wheat and Bengalgram diets. The fortification of wheat with lysine and of Bengalgram with methionine, cystine and tryptophan did not alter brain weight and DNA content. While brain RNA, protein free alpha amino nitrogen (F alpha AN) and activities of enzymes of glutamic acid metabolism and related amino acid levels were restored, the activity of enzyme glutamine transferase and alanine concentration remained unaltered on various diets fed. The observations on 20% casein diet showed that levels were similar to those observed on 10% casein diet.

Amino Acids↗
PubMed1979

Metabolism of thyrotropin releasing hormone in brain extracts. Isolation and characterization of an imidopeptidase for histidylprolineamide.

An extract of porcine brain acetone powder incubated with thyrotropin-releasing hormone (TRH; pGlu-His-ProNH2) produces acid TRH (pGlu-His-Pro), histidine, and prolineamide. Fractionation of the brain extract by DEAE-cellulose chromatography produces three protein fractions which metabolize TRH. The activity of these fractions was characterized using TRH with a 3H-label on the histidine or proline as well as [His-3H]His-ProNH2. Fraction I contains pyroglutamate aminopeptidase and Fraction II contains TRH deamidase. Fraction III was found to contain a previously unrecognized enzyme which cleaves His-ProNH2 to histidine and proline. The histidylprolineamide imidopeptidase has been characterized. A competition study using a variety of compounds containing histidine or proline suggests that the best substrates for the imidopeptidase contain a free alpha-amino group on histidine and a blocked carboxyl group on proline, as is found in His-ProNH2. A survey of a variety of polypeptide hormones indicates that many of them inhibit the imidopeptidase activity. A kinetic study of the inhibition of the enzyme by adrenocorticotropic hormone (1-24) shows that the inhibition by polypeptide hormones is noncompetitive. We hypothesize that pituitary hormones may stimulate the production of (cyclo)-His-Pro by inhibiting alternate routes of TRH metabolism.

Animals↗
PubMed1976

Demonstration of pyroglutamylpeptidase and amidase activities toward thyrotropin-releasing hormone in hamster hypothalamus extracts.

Using a radioimmunoassay method for thyrotropin-releasing hormone, the presence of thyrotropin-releasing hormone-metabolizing activity in various hamster tissues was demonstrated. While there was substantial activity degrading thyrotropin-releasing hormone in hypothalamus, there was a notable absence of such activity in pituitary. The enzymatic activity in the hypothalamus was shown to be soluble and separable into two fractions. Analysis of the metabolic products formed by the two enzymes indicated that one possessed an amidase activity (less than Glu-His-Pro-NH2 leads to less than Glu-His-Pro) and the other possessed pyroglutamylpeptidase activity (less than Glu-His-Pro-NH2 leads to less than Glu+His-Pro-NH2). Other peptides containing NH2-terminal pyroglutamic acid or COOH-terminal amide groups did not block the hydrolysis of thyrotropin-releasing hormone, suggesting that the enzymes were specific. Some inhibitors preferentially blocked the activity of one or the other enzymes. Of possible biological significance is the observation that thyroid-stimulating hormone inhibited the amidase activity while hydrocortisone inhibited the pyroglutamylpeptidase activity.

Amidohydrolases↗
PubMed1976

Involvement of the glucose enzymes II of the sugar phosphotransferase system in the regulation of adenylate cyclase by glucose in Escherichia coli.

The nature of the interaction of glucose with toluene-treated cells of Escherichia coli leading to inhibition of adenylate cyclase was examined by the use of analogues. Those analogues with variations of the substituents about carbon atoms 1 or 2 (e.g. alpha-methylglucoside or 2-deoxyglucose) are inhibitory, and they are also substrates of the phosphoenolpyruvate-dependent sugar phosphotransferase system. Analogues with changes in other parts of the molecule (e.g. 3-O-methylglucose or galactose), L-glucose and several disaccharides and pentoses, do not inhibit adenylate cyclase and are not substrates of the phosphotransferase system. This correlation suggests some functional relationship between the adenylate cyclase and phosphotransferase systems. Further studies were done with mutants defective in glucose enzymes II of the phosphotransferase system (designated GPT and MPT); these two activities are measured by phosphorylation of alpha-methyl-glucoside and 2-deoxyglucose, respectively. The wild-type parent phosphorylates both analogues, and both inhibit adenylate cyclase. In the GPT- mutant, alpha-methylglucoside does not inhibit adenylate cyclase and is not phosphorylated, while 2-deoxyglucose is inhibitory and phosphorylated. In the GPT- MPT- double mutant, adenylate cyclase activity is present, but neither alpha-methylglucoside nor 2-deoxyglucose inhibits adenylate cyclase, and neither sugar is phosphorylated. These studies demonstrate that glucose inhibition of adenylate cyclase in toluene-treated cells requires an interaction of this sugar with either the GPT or mpt enzyme II of the phosphotransferase system.

Adenylyl Cyclases↗