• P Roychowdhury

      Articles written in Journal of Biosciences

    • A comparative study of 5’nucleotidase and alkaline phosphatase in human placenta during development

      A S Chakraborti P Roychowdhury A Das M Mukherjea

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      Activities and a few properties of alkaline phosphatase and 5’-nucleotidase were compared in the developing human placenta. Both the enzymes were mostly membrane-bound and displayed similar developmental patterns with the highest activities at 24/26 weeks of the placenta. L-Phenylalanine, L-tryptophan and L-leucine were inhibitors of alkaline phosphatase, whereas they had no effect on the 5’-nucleotidase. Alkaline phosphatase from a late stage of gestation appeared to be almost heat-stable. An appreciable part of 5’-nucleotidase was also resistant to heat inactivation and this fraction varied with gestational age of the tissue. For both the enzymes, Vmax changed without alteringKm values with periods of gestation. Ca2+, Mg2+ and Mn2+ ions stimulated the alkaline phosphatase activity and Hg2+, Zn2+, Cu2+, Ni2+ were inhibitory. 5’-Nucleotidase was not activated by any of these cations. EDTA and Concanavalin A inhibited both the enzymes, although the extent of inhibition was different and also varied with gestation.

    • Molecular structure of troponin C from chicken skeletal muscle at 3Å resolution

      M Sundaralingam R Bergstrom G Strasburg S T Rao P Roychowdhury M Greaser B C Wang

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      Troponin C is the Ca2+-binding subunit of the troponin complex and is involved in the calcium control of muscle contraction. The X-ray structure of chicken TnC has been determined at 3Å resolution using a single heavy atom derivative and application of a novel phase improvement and phase extension procedure. The protein has an unusual dumbbell-shape with a length of about 70A. The N- and C-domains are connected by a single long α-helix of about 9 turns. Two metal binding sites (the Ca2+-Mg2+ sites) in the C-domain are occupied by metal ions in the crystals and the helix-loop-helix Ca2+ -binding folds are very similar to those in other known Ca2+ -binding proteins. In contrast, the Ca2+ -specific sites in the N-domain appear unoccupied and the two putative Ca2+ -binding folds have a vastly different structural arrangement. The conformational rearrangements in the N-domain upon Ca2+ binding are believed to be the trigger for a cascade of protein-protein interaction alterations which lead to muscle contraction.

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