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Biomedical subjects

C Prasad

Publications and source records attributed to C Prasad.

At least 181 records · Page 10Linked to original sources
PubMed1975

Initiation by methionine of mouse immunoglobulin light chain containing NH-2terminal pyroglutamic acid.

The mechanism of biosynthesis of NH2-terminal pyroglutamic acid has been studied in a mouse plasmacytoma (RPC-20) which produces an immunoglobulin light (lambda) chain containing NH2-terminal pyroglutamic acid. To this end, initation of lambda chain synthesis in plasmacytoma cell suspensions has been investigated. The analysis of radioactive lambda chain synthesis by these cells was accomplished with an antibody preparation specific for the precipitation of lambda chain protein from total plasmacytoma protein. NH2-terminal analysis of plasmacytoma cells labeled with [35S]methionine showed that the ratio of radioactivity in NH2-terminal methionine to total incorporation in lambda chain was greater at 2 min of labeling than at 60 min. However, such a pattern of transient labeling of the NH2 terminus of the lambda chain was not obtained when cells were incubated with tritiated leucine, arginine, or tryptophan. The data indicate that methionine is the initiator amino acid for the synthesis of lambda chain containing NH2-terminal pyroglutamic acid.

Amino Acid Sequence↗
PubMed1974

Deficiencies or excesses of metabolites interfering with differentiation.

Auxotrophic mutants of Bacillus subtilis need much higher concentrations of the required adenine, nicotinic acid, riboflavin, thiamine, or tryptophan for optimal sporulation than for maximal growth. Acetate can partially replace thiamine, indicating the importance of the pyruvate dehydrogenase system for differentiation. A glycerol-requiring mutant can sporulate only if its cells contain a small concentration of L-alpha-glycerol phosphate during development. This can best be achieved by excess (>/=5 mM) of extracellular alpha-glycerol phosphate, which enters B. subtilis very slowly. The results show that both biosynthetic and catabolic enzymes are often needed to maintain the precise balance of metabolites required for differentiation. Mutants unable to catabolize fructose 6-phosphate, glucose 6-phosphate, or alpha-glycerol phosphate do not sporulate as long as these compounds accumulate inside the cells; their development is blocked before prespore septa have formed.

Bacillus subtilis↗
PubMed1974

Cell lysis of Bacillus subtilis caused by intracellular accumulation of glucose-1-phosphate.

Mutants deficient in both glucose-6-phosphate dehydrogenase and phosphoglucose isomerase lysed 4 to 5 h after growth in nutrient medium containing glucose, or after prolonged incubation if the medium contained galactose. The lysis could be prevented by the addition of any other rapidly metabolizable carbon source such as fructose, glucosamine, or glycerol. The glucose-induced lysis was also abolished by introduction of a third mutation lacking phospho-glucose mutase activity but not by a third mutation lacking uridine diphosphate-glucose pyrophosphorylase or teichoic acid glucosyl transferase activity. Galactose-induced lysis was prevented only if the additional mutation abolished the uridine diphosphate-glucose pyrophosphorylase activity. The results showed that lysis was caused by the intracellular accumulation of glucose-1-phosphate, which in turn inhibited at least one of the two enzymes that convert glucosamine-6-phosphate to N-acetyl glucosamine-6-phosphate.

Autolysis↗
PubMed1974

Initiation of spore germination in Bacillus subtilis: relationship to inhibition of L-alanine metabolism.

The inhibitory effects of anthranilic acid esters (methyl anthranilate and N-methyl anthranilate) on the l-alanine-induced initiation of spore germination was examined in Bacillus subtilis 168. Methyl anthranilate irreversibly inhibited alanine initiation by a competitive mechanism. In its presence, the inhibition could be reversed only by the combined addition of d-glucose, d-fructose, and K(+). Both l-alanine dehydrogenase and l-glutamate-pyruvate transaminase, enzymes which catalyze the first reaction in l-alanine metabolism, were competitively inhibited by methyl anthranilate. The K(i) values for germination initiation (0.053 mM) and of l-glutamate-pyruvate transaminase (0.068 mM) were similar, whereas that for l-alanine dehydrogenase (0.4 mM) was six to seven times higher. Since a mutant lacking l-alanine dehydrogenase activity germinated normally in l-alanine alone, it is speculated that the major pathway of l-alanine metabolism during initiation may be via transmination reaction.

Alanine↗
PubMed1972

Initiation of spore germination in glycolytic mutants of Bacillus subtilis.

Enzyme activities of glycolysis and glyconeogenesis are present in spores of Bacillus subtilis, the rate-limiting step of glucose (GLC) metabolism being its phosphorylation. GLC allows initiation of germination in the presence of fructose (FRU) and asparagine (ASN), not because it is used via the Embden-Meyerhof path, but because it is oxidized in the nonphosphorylated form via the spore-specific GLC dehydrogenase. Spores of mutants lacking GLC-phosphoenolpyruvate transferase, FRU-6-P-kinase, or phosphoglucoisomerase activity can still be initiated by the above substrate combination. Furthermore, GLC can be replaced by 2-deoxy-GLC, which is also oxidized by GLC-dehydrogenase, but not by alpha- or beta-methylglucoside, which are not substrates of this enzyme. GLC probably acts by reducing nicotinamide adenine dinucleotide (or nicotinamide adenine dinucleotide phosphate), which is used for some metabolic reaction other than the cytochrome-linked electron transport system, since inhibitors of this system do not inhibit initiation. Spores of a mutant lacking FRU-1-P-kinase activity can no longer be initiated by GLC+FRU+ASN, but they do respond to the combination of GLC+mannose+ASN. Since spores of a FRU-6-P-kinase (or phosphoglucoisomerase) mutant can still respond to either FRU or mannose, FRU-6-P (or some derivative) apparently is needed for initiation (in addition to reduced nicotinamide adenine dinucleotide and an amino donor). Alanine can initiate germination in spores of all of the above mutants, indicating that it can form all required compounds. However, in a mutant lacking P-glycerate kinase activity, alanine initiates only after a long lag and at a slow rate, indicating that some compound in the upper metabolic subdivision is required for initiation, in agreement with the above findings. All initiating agents of B. subtilis probably produce the same required compound(s) by different metabolic routes.

Adenosine Triphosphate↗
PubMed1970

Tryptophan catabolism during sporulation in Bacillus cereus.

1. Two intermediates of tryptophan catabolism were isolated from a sporulating culture of Bacillus cereus and identified as anthranilic acid and kynurenine by their spectral properties. 2. During sporulation the rate of formation of anthranilic acid and kynurenine by whole cells increased and reached a maximum at the pre-spore stage. 3. The specific activities of tryptophan pyrrolase and formylase also increased during sporulation and exhibited a maximal activity at the pre-spore stage. 4. Kynureninase activity reached a maximum during early stages of sporulation and then started to decline. 5. There was a net increase in the activity of tryptophan pyrrolase when cells were grown in the presence of l-tryptophan or dl-kynurenine. 6. The cultures exhibited the maximal activity of kynureninase 2h earlier in the presence of dl-kynurenine whereas l-tryptophan delayed the appearance of the maximal activity by 2h. 7. The omission of glucose from the medium had no effect on the pattern of development of tryptophan pyrrolase during growth and sporulation. 8. On the addition of tryptophan to a chemically defined medium no significant change in the pattern of development of tryptophan pyrrolase was observed.

Bacillus cereus↗
PubMedDate not supplied

Thyrotropin-releasing hormone metabolism is attenuated in the cerebrospinal fluid of the human neonate.

The present study was designed to investigate the ontogeny of thyrotropin-releasing hormone (TRH) metabolism in human cerebrospinal fluid (CFS). The activity of pyroglutamate aminopeptidase (EC 3.4.11.8), the major enzyme catalyzing TRH metabolism in human CSF, was measured in CSF of 11 premature infants (gestational age, 29-39 weeks; birth weight, 1774 +/- 274 g), 8 newborn infants (term delivery; birth weight, 3648 +/- 240 g), and 11 adults (mean age, 29.6 +/- 1.5 years). Pyroglutamate aminopeptidase activity in CSF of premature and newborn infants was significantly lower (p less than 0.05) than that of adult CSF. These observed differences in the enzymatic activities were not due to changes in the affinity of the enzyme for its substrate TRH or the presence of enzyme inhibitor(s)/stimulator(s).

Adult↗
PubMedDate not supplied

Cyclo(His-Pro) and the development of tolerance to the hypothermic effect of ethanol.

Acute intraperitoneal administration of ethanol to rats causes a dose-dependent transient hypothermia. On repeated exposure, however, rats develop tolerance to hypothermic effects of ethanol. Cyclo(His-Pro), an endogenous brain peptide, modifies both acute and chronic themomodulatory effects of alcohol. For example, a) acute pretreatment of rats with increasing amounts of cyclo(His-Pro) produces a progressive decrease in ethanol hypothermia, and b) chronic cyclo(His-Pro) administration augments the development of tolerance to hypothermic effects of alcohol. While the mechanism of cyclo(His-Pro) action is not clear, these data are interpreted to suggest that this peptide may play important roles in ethanol intoxication, preference, tolerance, and/or addiction.

Acetaldehyde↗
PubMedDate not supplied

Distribution and metabolism of cyclo (His-Pro): a new member of the neuropeptide family.

Cyclo (His-Pro) is a biologically active cyclic dipeptide derived from thyrotropin-releasing hormone by its limited proteolysis. We have developed a specific radioimmunoassay for this cyclic peptide and shown its presence throughout rat and monkey brains. The normal rat brain concentration of cyclo (His-Pro) ranged from 35-61 pmols/brain. The elution profiles of rat brain cyclo (His-Pro)-like immunoreactivity and synthetic radioactive cyclo (His-Pro) following gel filtration, ion-exchange chromatography, and high pressure liquid chromatography were similar. An analysis of the regional distribution of cyclo (His-Pro) and TRH in rat and monkey brains exhibited no apparent precursor-product relationship. The possible additional factors determining regional differences in the endogenous cyclo (His-Pro) concentrations are discussed. The endogenous levels of brain cyclo (His-Pro) were elevated when rats were made either hypothyroid by surgical thyroidectomy or forced to drink alcohol for six weeks. These studies demonstrate that cyclo (His-Pro) is present throughout the central nervous system in physiologically relevant concentrations which can be modulated by appropriate physiological and pharmacological manipulations. These data in conjunction with earlier reports of multiple biological activities of exogenous cyclo (His-Pro), suggest that endogenous cyclo (His-Pro) is a biologically active peptide and it may play a neurotransmitter or neuromodulator role in the central nervous system.

Alcoholism↗
PubMedDate not supplied

Evidence for the presence of immunoreactive histidyl-proline diketopiperazine [cyclo (His-Pro)] in the adult human brain.

The current study was undertaken to evaluate the presence of cyclo (His-Pro) in adult human brain tissues obtained at autopsy. We found evidence for immunoreactive cyclo (His-Pro), which diluted in parallel to the radioimmunoassay standard curve and which had mobility on HPLC that was similar to synthetic cyclo (His-Pro), in several regions of the adult human brain. Whereas the levels of cyclo (His-Pro) in the pituitary stalk-median eminence were high (2.2 ng/mg protein), the concentrations in the whole hypothalamus were much lower (0.105 ng/mg protein). Among the extrahypothalamic brain regions examined, the levels of cyclo (His-Pro) were highest in the cerebellar hemisphere (0.168 ng/mg protein) and olfactory bulbs (0.180 ng/mg protein) and were lowest in the hippocampus (0.080 ng/mg protein) and occipital cortex (0.079 ng/mg protein). Thus, immunoreactive cyclo (His-Pro) has widespread distribution in the adult human brain and the potential exists for this cyclic diepeptide to play a role in human brain function.

Adolescent↗
PubMedDate not supplied

Distribution and characterization of cyclo (His-Pro)-like immunoreactivity in anuran (frog) skins.

The distribution of cyclo (His-Pro)-like immunoreactivity in frog skins from seven frog species was examined. The chromatographic elution profile of cyclo (His-Pro)-like immunoreactivity in amphibian skins measured by radioimmunoassay corresponded precisely to that of [3H-Pro]-cyclo (His-Pro) after DEAE-Cellulose, Sephadex G-25 and high-pressure liquid chromatography. The concentrations of cyclo (His-Pro) in frog skins were much higher than the concentrations of TRH previously observed in skin and the concentrations of cyclo (His-Pro) in both brain and gastrointestinal tract.

Animals↗
PubMedDate not supplied

Localization of neuropeptide Y-like immunoreactivity in the cat hypothalamus.

The distribution pattern of neuropeptide Y-like immunoreactivity (NPY-Li) in cat hypothalamus was studied using avidin-biotin modification of immunocytochemical method. This study showed cell bodies containing NPY-Li in the periventricular and the infundibular nuclei and also a moderate number of neurons with NPY-Li in the ventromedial nucleus, an observation not reported in earlier studies. Fibers with NPY-Li were noted throughout the hypothalamus, but most prominently within the periventricular regions. The location of NPY cells within the hypothalamus suggests the possibility of an interaction with dopaminergic and other proopiomelanocortinergic neurons.

Animals↗
PubMedDate not supplied

The distribution pattern of alpha-MSH-like immunoreactivity in the cat central nervous system.

The distribution pattern of alpha-melanocyte stimulating hormone-like immunoreactivity (alpha-MSH-Li) was studied in cats using avidin-biotin modification of immunocytochemical method. Cell bodies containing alpha-MSH-Li were observed in the medial basal hypothalamus, especially in the infundibular nucleus, the lateral hypothalamus and near zona incerta. Fibers with alpha-MSH-Li extended beyond the hypothalamus, into the paraventricular nucleus of the thalamus, rostral amygdala, periaqueductal gray, locus ceruleus, parabrachial nucleus and medial nucleus of the nucleus tractus solitarius. Axons with alpha-MSH-Li were also seen diffusely in various cortical areas, but more extensively in the limbic cortical regions. The distribution pattern of the cell bodies and fibers containing alpha-MSH-Li bears several similarities to that seen in rats, but differs in that the alpha-MSH-Li was not observed in cell bodies in locations other than the medial basal and lateral hypothalamus.

Animals↗