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Biomedical subjects

R Prasad

Publications and source records attributed to R Prasad.

At least 325 records · Page 18Linked to original sources
PubMed1982

Effect of phophatidylcholine and phosphatidylethanolamine enrichment on the structure and function of yeast membrane.

The phospholipid composition of yeast plasma membrane was manipulated by two different methods: (i) by using two auxotrophic strains KA101 (cho1) and MC13 (Cho+) which required phospholipid bases for growth and (ii) by supplementing Saccharomyces cerevisiae (3059) cells with high concentration of choline or ethanolamine. It was possible to enrich the plasma membrane with phosphatidylcholine (PC) or phosphatidylethanolamine (PE) by both methods. The uptake of amino acids, e.g., glycine, glutamic acid, leucine, lysine methionine, phenylalanine, proline and serine, was significantly reduced in PC- or PE-enriched cells. However, the extent of reduction in transport was variable among different strains. A fluorescent probe, 1-anilino-8-naphthalene sulfonate (ANS), was used to monitor the structural changes induced by altered phospholipid composition. It was observed that the relative fluorescence intensity of bound ANS was decreased as a consequence of PC or PE enrichment. The decrease in fluorescence was probably associated with reduced number of available binding sites (n) and increased apparent dissociation constant (Kd). Furthermore, our results also suggest that a critical level of PE or PC is required for proper functioning of yeast membrane.

Amino Acids↗
PubMed1982

Effect of chronic cadmium treatment on the ascorbic acid status of the rat.

In rats chronically treated with varying doses of cadmium (Cd) (0.25, 0.50, 0.75 and 1.0 mg/kg body wt.), i.p., every alternate day for 7 weeks, a decrease in the ascorbic acid (AA) content of adrenals and liver was observed. In the adrenals AA depletion was significant and dose-dependent at all concentrations. In liver the decrease was significant only at a concentration of 0.75 and 1.00 mg/kg but the spleen did not show any change in AA content. Urinary excretion of beta2-microglobulin with increasing doses of Cd indicated progressive renal tubular damage. The decrease in tissue AA status was correlated with the severity of the renal tubular damage resulting in an inhibition of its reabsorption from the kidneys.

Adrenal Glands↗
PubMed1982

Effect of gamma-radiation on the structure and function of yeast membrane.

A decrease in the influx of several amino acids was observed following gamma-irradiation. At low dose (2.5 Gy), which does not affect cell survival, a stimulation in the uptake was visible; moreover, sulphydryl loss and lipid peroxidation were also evident. With further increase in the dose of radiation, a parallel increment in the loss of sulphydryl groups and production of malonaldehyde was observed. Radioprotectors like L-cysteine and dithiothreitol were shown to shield the radiation-induced loss of sulphydryl and damage to transport and survival. Reduced glutathione, on the other hand, exhibited protection at the level of sulphydryl damage only. N-ethylmaleimide, a well known hypoxic cell radiosensitizer, enhanced the radiosensitivity with respect to survival; it, however, had no effect on amino acid transport. Oxygen enhancement of radiation damage to transport and cell survival and the radioprotection by sodium formate under these circumstances, and more so by anoxia, were demonstrated. The results indicate that the manifestation of damage to membrane structure and function precedes any observable loss of survival.

Amino Acids↗
PubMed1982

Effect of vitamin B6 and B1 deficiencies on the intestinal uptake of calcium, zinc and cadmium.

A chronic vitamin B6 deficiency in rats resulted in a non-specific increase (44- 51%) in the in vitro intestinal uptake of both essential (Ca and Zn) and non-essential toxic metal (Cd) ions, whereas an acute B6-deficient state only affected the Zn uptake rate. In vitamin B1-deficient animals, a specific decrease (30-32%) was observed in Ca and Zn uptake with a 59% increase in the intestinal uptake of Cd. These altered metal ion uptake rates were probably not a result of hormonal disturbances due to the vitamin-deficient states.

Animals↗
PubMed1981

Distinct mechanisms of hypoxanthine and inosine transport in membrane vesicles isolated from Chinese hamster ovary and Balb 3T3 cells.

Both enzyme-mediated group translocation and facilitated diffusion have been proposed as mechanisms by which mammalian cells take up purine bases and nucleosides. We have investigated the mechanisms for hypoxanthine and inosine transport by using membrane vesicles from Chinese hamster ovary cells (CHO), Balb/c 3T3 and SV3T3 cells prepared by identical procedures. Uptake mechanisms were characterized by analyzing intravesicular contents, determining which substrates could exchange with the transport products, assaying for hypoxanthine phosphoribosyltransferase activity, and measuring the stimulation of uptake of hypoxanthine by phosphoribosyl pyrophosphate (PRib-PP). We found that the uptake of hypoxanthine in Balb 3T3 vesicles was stimulated 3--4-fold by PRib-PP. The intravesicular product was predominantly IMP. The hypoxanthine phosphoribosyltransferase activity copurified with the vesicle preparation. These results suggest the possible involvement of this enzyme in hypoxanthine uptake in 3T3 vesicles. In contrast to the 3T3 vesicles, CHO vesicles prepared under identical procedures did not retain hypoxanthine phosphoribosyltransferase activity and did not demonstrate PRib-PP-stimulated hypoxanthine uptake. The intravesicular product of hypoxanthine uptake in CHO vesicles was hypoxanthine. These results and data from our kinetic and exchange studies indicated that CHO vesicles transport hypoxanthine via facilitated diffusion. An analogous situation was observed for inosine uptake; CHO vesicles accumulated inosine via a facilitated diffusion mechanism, while in the same experiments SV3T3 vesicles exhibited a purine nucleoside phosphorylase-dependent translocation of the ribose moiety of inosine. Vesicles prepared from a CHO cell line temperature-sensitive for hypoxanthine uptake (Azarts) showed a temperature-sensitivity in Km for uptake parallel to that of the intact cells. This suggests that the defect in Azarts may be caused by a missense mutation in the gene coding for the hypoxanthine transport carrier.

Animals↗
PubMed1981

Nutrient transport in a bovine lens epithelial cell line.

A bovine calf lens epithelial cell line (CLE-1) that synthesizes crystallin has been established in culture and some of its transport properties have been characterized using both cells and membrane vesicles derived from them. The membrane vesicles fractionate with high recovery of plasma membrane markers, showing a 40-fold purification of 5'-AMPase and a 20-fold decrease in the specific activity of the mitochondrial marker enzyme succinic dehydrogenase relative to a cell homogenate. Transport sites demonstrated higher specific activity than has been seen in vesicles from cell lines studied previously. The uptake of alpha-amino isobutyric acid (AIB) (an alanine analog) by CLE-1 cells is stimulated four- to fivefold by Na+ and exhibits a Km of 5.4 mM with a Vmax of 50 pmoles/min.microgram of cell protein. The uptake of leucine was not Na+ stimulatable. The uptake of AIB by the cells was reduced by 43% at confluence. Thus, the cell density dependent behavior of the uptake of the alanine amino acid family in CLE-1 is similar to that of various fibroblast cells. The Na+ caused a threefold stimulation of AIB uptake in the membrane vesicles, while vesicular uptake of leucine was unaffected by Na+. The uptake of adenine, guanine, uridine, and guanosine was also tested in these vesicles. The substrates were rapidly accumulated, came to a steady state distribution within 1-2 minutes, and were recovered as the unaltered compounds after uptake.

Amino Acids↗
PubMed1980

Charge forms of Wistar rat alpha-lactalbumin. A contradiction.

alpha-Lactalbumin was purified from the milk of Wistar rats and was compared to that obtained from Fisher 344 rats. alpha-Lactalbumin isolated from the Wistar rat exists as two forms which differ in their sialic acid content, as the desialyated forms migrate to one identical position on polyacrylamide gels. These two charge forms are identical with the charge Forms II and III previously characterized from Fisher rat alpha-lactalbumin. No evidence was found to verify previous reports that one form of the Wistar rat alpha-lactalbumin had a higher molecular weight than the other form. Indeed, the molecular weights and the amino acid compositions of the two forms of Wistar rat alpha-lactalbumin are identical. In addition, the partial amino acid sequence at the NH2-terminal end and the amino acid composition of the COOH-terminal cyanogen bromide peptide of the two forms are identical. The results in this study contradict those reported previously and show that rat alpha-lactalbumin exists as a single molecular weight species.

Amino Acid Sequence↗
PubMed1980

The structure of the asparagine-linked carbohydrate unit of rat alpha-lactalbumin.

Rat alpha-lactalbumin is unique in contrast to alpha-lactalbumin isolated from other species in that it exists in three charge forms. Each form contains carbohydrate and is active in the lactose synthetase reaction. Form II comprises about 80% of the total alpha-lactalbumin and contains a single heteropolysaccharide unit which is attached to the polypeptide chain at Asn45. The detailed structure of this unit was ascertained using specific exoglycosidases, endoglycosidases, and methylation analysis. The following structure is proposed for the heteropolysaccharide unit: (formula: see text).

Animals↗
PubMed1980

Effect of pyridoxine deficiency on Litomosoides carinii infection in albino rats.

Pyridoxine deficiency has been induced in albino rats at the weanling or neonatal stages. Exposure of the vitamin-deficient rats to the infective larvae of Litomosoides carinii resulted in no development or establishment of the parasite in the host. Although the food consumption of the pair-fed group was necessarily restricted to that of the deficient group, the susceptibility of the animals of the pair-fed group receiving the normal vitamin intake resembled that of the control group. The humoral immune response to the infection in the pair-fed controls as measured by indirect haemagglutination, was inhibited compared to that in the controls. This inhibition was more severe in the vitamin-deficient animals.

Animals↗