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Biomedical subjects

P Harikumar

Publications and source records attributed to P Harikumar.

At least 19 recordsLinked to original sources
PubMed2004

Autolytic degradation of chicken intestinal proteins.

Data on the exhaustive degradation of chicken intestinal proteins by endogenous proteases, which could be utilized as a means to prepare protein hydrolysate, is reported in the present paper. Chicken intestine possesses proteolytic activities (cathepsin B, D, H, L, aminopeptidases and alkaline proteases) comparable to that in organ tissues like liver and spleen, which could degrade the tissue proteins extensively. The autolytic degradation was found to be optimum at pH 2.5 and 60 degrees C. Analysis by SDS-PAGE showed a time dependent degradation of proteins to low molecular weight (<10 kDa) products. Kinetic studies employing specific inhibitors indicated that the degradation (90-94%) of proteins at acidic pH is governed largely by pepstatin sensitive proteases. The acidic extract of the tissue was found to hydrolyse albumin, casein and soybean proteins efficiently. Results point to the possible application of tissue autolysis for obtaining protein hydrolysates from chicken intestine. Chicken intestine could also serve as a potential source of much needed proteolytic enzymes for food and pharmaceutical applications.

Animals↗
PubMed1996

Vitamin A-deficiency and its effects on the lysosomal enzymes of fish.

The effect of vitamin A-deficiency on the structural integrity of lysosomes in the skeletal muscle and skin of Heteropneustes fossilis, a dehydroretinol-rich freshwater siluroid used in pisciculture, has been evaluated. Dietary stress was found to cause enhanced release of acid hydrolases from both skeletal muscle and skin tissues. The results indicate that the regulation of lysosomal membrane stability in these tissues is a function of vitamin A.

Acid Phosphatase↗
PubMed1993

Preparation of membrane vesicles from kidney cortex lysosomes using amino acid methyl ester.

A procedure for the preparation of intact membrane vesicles from kidney cortex lysosomes is reported. Highly purified preparations of lysosomes were isolated from rat and buffalo kidney cortex by Percoll density gradient centrifugation. The lysosomal membrane vesicles were prepared by osmotic rupture of the organelle with glutamate dimethyl ester. The integrity of the vesicles was demonstrated by their capacity to hold K+ and maintain H+ gradients.

Animals↗
PubMed1993

Purification and characterization of an alkaline proteinase from kidney cortex lysosomes.

An alkaline proteinase was purified to apparent homogeneity from buffalo (Bubalus bubalis) kidney cortex lysosomes by affinity chromatography on STI sepharose 4B and gel filtration over Sephadex G-100. The molecular weight of the enzyme was 17,000 and 21,000 by gel filtration and SDS/PAGE respectively. The purified enzyme was optimally active at pH 8.5-9.0 at 50 degrees C and hydrolysed synthetic substrates of chymotrypsin but not those of elastase or trypsin. It was inhibited by serine proteinase inhibitors like soybean trypsin inhibitor, limabean trypsin inhibitor and phenylmethyl sulphonyl fluoride. Immunologically, the enzyme was similar to chymotrypsin. The amino acid composition showed high content of acidic amino acids. This protein was detected in kidney, liver, spleen, pancreas and heart.

Amino Acid Sequence↗
PubMed1992

Assessment of the genotoxic potential of riboflavin and lumiflavin. A. Effect of metabolic enzymes.

The mutagenic potential of riboflavin and its photodegradation product lumiflavin was evaluated using the umu test, SOS chromotest and Ames Salmonella assay. Both riboflavin and lumiflavin by themselves were found to be non-mutagenic. On treatment with rat liver microsomal enzymes (S9) or caecal cell-free extract (CCE), lumiflavin acquired mutagenicity, while the status of riboflavin remained unaffected. Activation of lumiflavin by metabolic enzymes was found to result in an alteration of its spectral characteristics.

Alkaline Phosphatase↗
PubMed1992

Assessment of the genotoxic potential of riboflavin and lumiflavin. B. Effect of light.

On exposure to visible light, riboflavin and lumiflavin produced reactive oxygen species such as singlet oxygen and superoxide radicals. The reaction was found to be time- and concentration-dependent. Both riboflavin and lumiflavin, upon illumination, showed mutagenic response in the umu test as well as in the Ames/Salmonella assay with Salmonella typhimurium TA102. The mutagenic response was partially abolished by superoxide dismutase while sodium azide did not have any effect. No mutagenicity was observed if the compounds were not illuminated. The results suggested the involvement of superoxide radicals in light-induced mutagenicity of riboflavin as well as lumiflavin.

Azides↗
PubMed1989

Evidence for the occurrence of an alkaline proteinase in kidney cortex lysosomes.

A novel alkaline endoproteinase optimally active at pH 8.5 has been detected in highly pure preparations of buffalo kidney cortex lysosomes. The enzyme has been partially purified (90-fold) by solubilization with octylglucoside, acid precipitation and chromatography over DEAE sephacel and sepharose 6B. The alkaline proteinase, resistant to known inhibitors of lysosomal cathepsins is inhibited by soyabean trypsin inhibitor and phenyl methyl sulphonyl fluoride indicating that the enzyme is a serine proteinase.

Animals↗
PubMed1985

Influence of starvation on the intra-lysosomal proteolysis in rat liver.

Starvation induced changes in the intralysosomal proteolysis in rat liver were assessed in terms of the degradation of intravenously administered [131I]-human serum albumin 30 min after injection. Fasting for five days resulted in nearly 11% increase in the endocytic uptake of the labeled protein in lysosome rich fraction. However, the rate of degradation of internalized protein measured in terms of TCA soluble products showed a distinct decline in starved animals as compared to fed controls. The observed decrease in proteolysis was reversed completely by refeeding the starved rats for 10 days. The restoration of the degradation profiles in fasted animals was also accomplished by isolating lysosomes at a post injection period of 90 min. The results indicated that the starvation induced decrease in proteolysis was a consequence of delayed fusion of lysosomes and the phagosome containing the labeled protein.

Animals↗
PubMed1983

The lysosomal proton pump is electrogenic.

Lysosomes were purified approximately 40-fold from rat kidney cortex by differential and Percoll density gradient centrifugation. In a sucrose medium, the lysosomes quenched the fluorescence of the potential sensitive dye diS-C3-(5) (3,3'-dipropylthiocarbo-cyanine iodide) in a time-dependent manner, indicating that the dye accumulates within the lysosomal interior. After treatment of the lysosomes with valinomycin, the dye fluorescence displayed a logarithmic dependence upon the external K+ concentration; thus, the fluorescence signal provides a semiquantitative measure of the lysosomal membrane potential (delta psi). In the absence of valinomycin, lysosomal quenching of diS-C3-(5) fluorescence was partially reversed by agents which collapse the lysosomal pH gradient (ammonium sulfate, chloroquine, and K nigericin), suggesting that the proton gradient across the lysosomal membrane contributes to delta psi. A rapid increase in diS-C3-(5) fluorescence, indicative of an increase in delta psi, was observed upon the addition of Mg-ATP to the lysosomes. The ATP-dependent fluorescence change was inhibited by protonophores, K valinomycin, permeable anions, and N-ethylmaleimide, but was unaffected by ammonium sulfate, K nigericin, or sodium vanadate. Oligomycin had no effect at concentrations below 2 micrograms/ml; at higher concentrations, oligomycin partially inhibited the fluorescence response to Mg-ATP, but it also inhibited the fluorescence response to K valinomycin, suggesting that it had modified the permeability of the lysosomal membrane. Dicylohexylcarbodiimide behaved similarly to oligomycin. Mg-ATP also altered the lysosomal distribution of 86Rb+ (in the presence of valinomycin) and S[14C]CN-, consistent with an increase in the potential of the lysosomal interior of 40-50 mV. The results demonstrate that the lysosomal proton pump is electrogenic.

Adenosine Triphosphatases↗
PubMed1979

Response of heterogenous rat liver lysosome populations to starvation and refeeding.

Starvation-induced alterations in liver lysosomes and their recovery pattern following refeeding were investigated. Fasting of adult rats for five days caused an increase in 'free' activities of acid hydrolyses in liver homogenates and loss in sedimentation of one of the heterogenous populations of lysosomes that could be isolated by differential centrifugation. Isopycnic sucrose gradient centrifugation revealed a decrease in the median and modal equilibration densities of all the forms of lysosomes in response to the dietary deprivation. Further, starvation also evoked a distinct bimodal distribution in a population that was rich in acid phosphatases, beta-galactosidase and N-acetyl-beta-glucosaminidase. Realimentation of starved animals for 10 days was found to restore the enzyme levels and the sedimentation characteristics to normal profiles.

Acetylglucosaminidase↗
PubMed1975

Regulatory responses of arginine deiminase in whole cells of Clostridium sporogenes.

Arginine deiminase (EC 3.5.3.6) has been shown to have regulatory properties. The activity was observed to be sigmoidal with respect to substrate concentrations. Addition of histidine to the system caused the abolition of sigmoidal responses. The regulatory properties of the enzyme as well as the desensitising action of histidine could also be demonstrated with whole cell suspensions. The pH of the system also seemed to influence modulations in the enzyme.

Arginine↗