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Biomedical subjects

A K Rai

Publications and source records attributed to A K Rai.

34 records · Page 2Linked to original sources
PubMed1984

Interaction of constituent subunits in ribulose 1,5-bisphosphate carboxylase from Aphanothece halophytica.

Ribulose 1,5-bisphosphate carboxylase-oxygenase (RuBisCO) from the halophilic cyanobacterium, Aphanothece halophytica, dissociates into catalytic core (large subunit A oligomer) and small subunit B under low ionic strength during sucrose density gradient centrifugation. Supplementation of KCl, NaCl, or K2SO4 ( [I] = 0.3 M) partly prevents the dissociation, the preventive effect of divalent cation salts such as MgCl2 and CaCl2 being more effective than monovalent cation salts. RuBisCO with its higher-plant-type molecular form can be isolated from the cyanobacterial extracts using gradient medium containing 0.3 M KCl, 20 mM MgCl2, and 10 mM CaCl2. The isolated enzyme contains large subunit A and small subunit B in a molar ratio of approximately 1:1, estimated from the densitometric scanning of Coomassie blue-stained gels. During the second sucrose density gradient centrifugation to remove minor contaminants, a small amount of subunit B is depleted from the holoenzyme. Determination of the molecular weight by equilibrium centrifugation and electron microscopic observation have confirmed that the cyanobacterial RuBisCO has an A8B8-type structure. The enzyme activity per se is found to be sensitive to concentrations of salts, and small subunit B is obligatory for the enzyme catalysis. It has been shown that the more the enzyme activity is inhibited by salts, the tighter the association of subunit B becomes. It is likely that the active enzyme retains the loose conformational structure to such an extent that the dissociable release of subunit B from the holoenzyme in vivo is not allowed.

Calcium Chloride↗
PubMed1981

ATP-dependent uptake of nitrate in Nostoc muscorum and inhibition by ammonium ions.

A high rate of nitrate uptake was observed in Nostoc muscorum when cells were grown on elemental nitrogen as compared to that when they were grown on nitrate or ammonium. The uptake of nitrate was light dependent. However, supplementation with ATP (50 microM) stimulated nitrate uptake both in light and darkness. ADP, under similar conditions had no effect. 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), 2-n-heptyl-4-hydroxyquinoline, (HOQNO) and KCN inhibited nitrate uptake in light which could be partially reversed by addition of ATP. Inhibition by carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP), an uncoupler of photophosphorylation, was complete and could not be restored by the addition of ATP. N,N'-dicyclohexylcarbodiimide (DCCD), a specific inhibitor of ATPase, blocked nitrate uptake in the presence or absence of externally added ATP. Although no nitrate uptake was observed under anaerobic conditions in dark, addition of ATP resulted in uptake of nitrate, which was similar in magnitude to that observed under aerobic condition in the light, and was inhibited by DCCD. Ammonium ions inhibited the uptake of nitrate in the absence of ATP but in its presence there was simultaneous uptake of nitrate and ammonium ions. However, uptake of ammonium ions alone was not affected by presence or absence of ATP in the external medium. It was concluded that nitrate ion uptake was energy dependent and may be linked with a proton gradient which can be formed either by photophosphorylation or ATP hydrolysis.

Adenosine Triphosphate↗
PubMed1979

Cutaneous water loss and respiration rates of various breeds of sheep at high ambient temperatures.

The sweating and respiratory rates in rams of Rambouillet (R), Chokla (C), Malpura (M), R x C and R x M breed/breed crosses were recorded when housed in sheds or exposed to 20, 25, 30, 35 and 42 degrees C ambient temperatures in a climatic chamber. The sweating (cutaneous moisture) was higher (P less than 0.05) in Rambouillet and its crosses than the natives, the Malpura sheep producing the least sweat at all temperatures. There was no breed difference in the response of increase in sweating up to 35 degrees C but at 42 degrees C the Chokla showed a considerable increase. Sweating was more pronounced on the shoulder than on the mid-side region. Sweating and respiratory rates increased (P less than 0.05) with the increase in ambient temperature. The Rambouillet exhibited the highest increase in respiration rate at 25 degrees C and the trend continued up to 42 degrees C. The relationship between fleece characteristics, evaporative heat loss tolerance of sheep is dicussed.

Animals↗
PubMed1976

Lipids in the skin of a cat-fish Heteropneustes fossilis (Bloch) (Heteropneustidae, Pisces). A histochemical investigation.

Localization and characterization of different lipids in the cellular constituents of the skin of Heteropneustes fossilis has been made using several histochemical techniques. High contents of cholesterol, its esters and phospholipids have been correlated with the metabolically active state of the basal cells undergoing cell proliferation and differentiation. The polygonal cells in the outermost layer of the epidermis, though rich in phospholipid contain small amounts of cholesterol and its esters. This has been correlated with the metabolically less active state of theses cells. Neutral lipids and phospholipids in the polygonal cells of the outermost layer may contribute to the contents of surface slime and act as an efficient barrier for the penetration of water through the skin. The deposits of neutral lipids in the subcutis may provide energy during the period of fasting, act as a barrier for water diffusion through the skin and serve as shock absorbing pads protecting the fish from mechanical injury.

Animals↗
PubMedDate not supplied

Pharmacokinetics, bioavailability and dosage regimen of sulphadimidine in camels (Camelus dromedarius) under hot, arid environmental conditions.

A two-way crossover study was conducted in young Bikaneri camels (aged between 12 and 18 months) during the hot summer season to determine the bioavailability, pharmacokinetics and dosage regimens of sulphadimidine (SDM). A dose of 100 mg.kg-1 of SDM was used to study both the intravenous and oral pharmacokinetics of the drug. Analysis of the intravenous data according to a two-compartment pharmacokinetic model revealed that SDM was well distributed in the body (Vd(area):0.862 L.kg-1), had an overall body clearance of 0.035 +/- 0.019 L.h-1.kg-1 and the elimination of half-lives was in the range of 14.2 to 20.6 h. The mean maximum plasma SDM concentration following oral administration was 63.23 +/- 2.33 micrograms.mL-1, which was achieved 24 h after the oral administration. The mean bioavailability of SDM following oral administration was approximately 100%. To achieve and maintain the therapeutically satisfactory plasma sulphadimidine levels of > or = 50 micrograms.mL-1, the optimum dosage regimen for camels following either intravenous or oral administration would be 110 mg.kg-1 as the priming dose and 69 mg.kg-1 as the maintenance dose, to be repeated at 24 h intervals.

Animals↗