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Biomedical subjects

V K Kalra

Publications and source records attributed to V K Kalra.

At least 73 records · Page 4Linked to original sources
PubMed1977

Different binding sites for entry and exit of amino acids in whole cells of Mycobacterium phlei.

On the basis of mutual inhibition of uptake with different amino acids in whole cells of Mycobacterium phlei, it was demonstrated that the binding site of proline was different from those of all other amino acids studied. Other groups of amino acids share a common binding site: lysine, histidine, and arginine; valine, leucine, and isoleucine; tryptophan, tyrosine, and phenylalanine; glutamic acid and aspartic acid. The exit and entry processes were studied for proline, glutamine, and glutamic acid. It was observed that in each case the entry and exit processes were mediated by different membrane sites.

Amino Acids↗
PubMed1976

Abnormal activation of sterol synthesis in lymphocytes of atherosclerotic-susceptible pigeons and heterozygous familial hypercholesterolemic patients.

Delipidated human sera enhances the incorporation of [2-14C]acetate, but not mevalonate, into digitonin-precipitable sterols of pigeon lymphocytes. Show Racer and White Carneau pigeons exhibit inherited differences in induction of sterol synthesis dissociated from inheritance of hypercholesterolemia. Moreover, lymphocytes of three familial hypercholesterolemic individuals, having serum cholesterol level in the normal range by drug therapy, exhibited a higher activation of sterol synthesis by delipidated sera when compared to cells of normal individuals. It is suggested that genetic abnormality in lymphocytes of familial hypercholesterolemic can be dissociated from hypercholesterolemia.

Acetates↗
PubMed1976

Different mechanisms of energy coupling for transport of various amino acids in cells of Mycobacterium phlei.

Whole cells of Mycobacterium phlei were shown to actively accumulate proline, leucine, lysine, tryptophan, histidine, glutamine, and glutamic acid to different steady state levels. The transport of proline, in contrast to that of other amino acids, was found to be insensitive to various respiratory inhibitors, e.g. cyanide, arsenate, azide, and sulfhydryl reagents. However, oxygen was an obligatory requirement for the uptake of proline, as well as for the other amino acids. The results indicate that the energy requirements for proline uptake are different from those of other amino acids. In contrast to the system from Escherichia coli, the mode of energy transduction for the uptake of proline, glutamine, and glutamic acid is different even though these amino acids are shock resistant in the M. phlei system.

Adenosine Triphosphate↗
PubMed1975

Energy-transducing membrane-bound coupling factor-ATPase from Mycobacterium phlei. I. Purification, homogeneity, and properties.

The membrane-bound coupling factor from Mycobacterium phlei was solubilized from membrane vesicles by washing with low ionic strength buffer or 0.25 M sucrose. The solubilized enzyme exhibited coupling factor, latent ATPase, and succinate oxidation-stimulating activity. Purification by affinity chromatography using Sepharose coupled to ADP yielded a homogeneous preparation of latent ATPase which was purified about 200-fold with an 84% yield in a single step. Purified latent ATPase exhibited coupling factor activity but no succinate oxidation-stimulating activity. The molecular weight of latent ATPase was determined to be 250,000 +/- 10,000 by Sephadex G-200 chromatography. The ATPase was unmasked by trypsin treatment and activated by Mg2+ ion. However, trypsin treatment inactivated the coupling factor activity in the purified enzyme, indicating that the catalytic sites for ATPase and coupling activity are different. Unlike mitochondrial ATPase, latent ATPase from M. phlei was not cold-labile. Of the nucleoside triphosphates, UTP, ITP, and epsilon-ATP (1-N6-ethenoadenosine triphosphate) were hydrolyzed to a lesser extent compared to ATP. Kinetic data showed that ADP acted as a competitive inhibitor of latent ATPase activity with a Ki of 5 x 10(-3) M. Uncouplers of oxidative phosphorylation and respiratory inhibitors did not affect the latent ATPase activity, while sodium azide (0.1 mM) inhibited the latent ATPase activity.

Adenosine Triphosphatases↗
PubMed1975

Effect of phospholipase A on active transport of amino acids with membrane vesicles of Mycobacterium phlei.

Active transport of proline remained unaffected in phospholipase A-treated electron transport particles from Mycobacterium phlei. However, the steady state level of proline was reduced 50 to 60% in phospholipase A-treated depleted electron transport particles that were devoid of membrane-bound coupling factor-latent ATPase activity. The decrease in the uptake of proline in the phospholipase A-treated depleted electron transport particles was not due to a change in the apparent K-m for proline, but it was related to the amount of phospholipid cleaved from the membranes. Restoration in the level of proline transport in phospholipase A-treated depleted electron transport particles was achieved by reconstituting these vesicles with diphosphatidylglycerol and phosphatidylethanolamine liposomes. Diphosphatidylglycerol was found to be most effective in the restoration of proline uptake. In contrast to the effect of phospholipase A treatment on proline transport, similar treatement of the electron transport particles or depleted electron transport particles failed to inhibit the active transport of either glutamine or glutamic acid. Studies with phospholipase A-treated membrane vesicles confirmed earlier findings that a proton gradient is not required for active transport of amino acids.

Adenosine Triphosphatases↗
PubMed1975

Effect of phospholipase A on the structure and functions of membrane vesicles from Mycobacterium phlei.

The phospholipid composition of the electron transport particles and coupling factor-depleted electron transport particles of Mycobacterium phlei are the same, but they differ in contents. The accessibility of partially purified phospholipase A to these membrane phospholipids was found to be different. Treatment of membranes of Mycobacterium phlei with phospholipase A impairs the rate of oxidation as well as phosphorylation. The inhibition of phosphorylation can be reversed by washing the membranes with defatted bovine serum albumin. The reconstitution of membrane-bound coupling factor-latent ATPase activity to phospholipase A-treated depleted electron transport particles and their capacity to couple phosphorylation to oxidation of substrates remained unaffected after phospholipase A treatment. However, the pH gradient as measured by bromthymol blue was not restored after reconstitution of phospholipase A-treated depleted electron transport particles with membrane-bound coupling factor-latent ATPase. These findings show that the phosphorylation coupled to the oxidation of substrates can take place without a pronounced pH gradient in these membrane vesicles. The dye 1-anilino-8-naphthalene sulfonic acid (ANS) exhibited low levels of energized and nonenergized fluorescence in phospholipase A-treated membranes. This decrease in the level of ANS fluorescence in phospholipase A-treated membranes was found to be directly related to the amount of phospholipids cleaved. The decrease in the energy-dependent ANS response in phospholipase A-treated electron transport particles, as compared with untreated electron transport particles, was shown to be a result of a change in the apparent K-d of the dye-membrane complex, and of a decrease in the number of irreversible or slowly reversible binding sites, with no change in the relative quantum efficiency of the dye. The decrease in ANS fluorescence in phospholipase A-treated particles appears to be due to a decrease in the hydrophobicity of the membranes.

Anilino Naphthalenesulfonates↗
PubMed1975

Purification and properties of membrane-bound coupling factor-latent ATPase from Mycobacterium phlei.

The membrane bound coupling factor-latent ATPase was solubilized from the membrane vesicles of Mycobacterium phlei by using 0.25 M sucrose or low ionic strength buffer. Purification of the solubilized enzyme by use of Sepharose-ADP conjugate gel yielded a homogenous preparation of latent ATPase which was purified about 216-fold in a single step with an 84% yield. The enzyme exhibits a specific activity of 39 mumoles of ATP hydrolyzed per min per mg protein. The purified enzyme exhibits coupling factor activity. Electrophoresis in two dissociating solvent systems indicates that the enzyme contains at least three major polypeptides of molecular weights 56,000, 51,000, and 46,000 daltons, and two minor polypeptides of 30,000 and 17,000 daltons. Equilibrium binding studies of ADP with purified coupling factor-latent ATPase reveal the presence of two nucleotide binding sites per molecule with an apparent Ka of 8.1 X 10(-5) M. By use of affinity chromatography, another latent ATPase has been isolated from the solubilized enzyme, which does not exhibit coupling factor activity.

Adenosine Diphosphate↗