• R D Dua

      Articles written in Journal of Biosciences

    • Mechanistic studies on carboxypeptidase A from goat pancreas Part I: Role of tyrosine residue at the active site

      R D Dua Kamlesh Gupta

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      Chemical modification of carboxypeptidase Ag1 from goat pancreas with Nacetylimidazole or iodine led to loss of enzymic activity. This loss in activity could be prevented when chemical modification was carried out in the presence of Β-phenylpropionic acid or substrate NCbz-glycyl-L-phenylalanine, thus suggesting a tyrosine residue at the active site. Chemical modification of tyrosine was confirmed by spectral and kinetic studies. While tyrosine modification destroyed peptidase activity, esterase activity of the enzyme remained unchanged thus indicating non-involvement of tyrosine residue in ester hydrolysis

    • Product stabilization of the two forms of carboxypeptidase A from buffalo pancreas

      Mira Sud R D Dua

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      The two forms of buffalo carboxypeptidase A lose a part of their activity when incubated at their optimal temperature. Both the forms are protected from heat denaturation by L-phenylalanine, one of the reaction products while the other reaction product hippuric acid provides only limited protection. It has also been shown that L-phenylalanine and hippuric acid bind at the same site of the enzyme and that the release of L-phenylalanine follows that of hippuric acid. On this basis, a new mechanism for the hydrolysis of acyldipeptides by carboxypeptidase A has been proposed

    • Mechanistic studies on carboxypeptidase a from goat pancreas — part II: Evidence for carboxyl group

      R D Dua Kamlesh Gupta

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      Studies with substrate analogues and the pH optimum indicated the involvement of carboxyl group in the active site of goat carboxypeptidase A. Chemical modification of the enzyme with 1-cyclohexyl-3-(2-morpholinoethyl) carbodiimide methoI -p-toluene sulphonate, a carboxyl specific reagent, led to loss of both esterase and peptidase activities. Protection studies showed that this carboxyl group was in the active site and was protected by Βp-phenylpropionic acid and glycyl-L-tyrosine. Kinetic studies also confirmed the involvement of carboxylic group because the enzyme modification with water soluble carbodiimide was a two step reaction which excluded the possibility of tyrosine or lysine which are known to give a one step reaction with this reagent

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