NOPR Collection:

Effect of arginine modifying reagents on pigeon liver fatty acids synthetase: Evidence for the presence of essential arginine residues at the β-ketoacyl reductase and enoyl -CoA reductase domain

2012-12-28T16:33:11Z

Title: Effect of arginine modifying reagents on pigeon liver fatty acids synthetase: Evidence for the presence of essential arginine residues at the β-ketoacyl reductase and enoyl -CoA reductase domain Authors: Mukherjee, Sanchita; Kaliyar, Sarvagya S Abstract: Pigeon liver fatty acid synthetase was inactivated by arginine modifying reagent, phenylglyoxal and 2,3 -butanedione. The inactivation of overall fatty acid synthetase was accompanied by the loss of β-ketoacyl reductase and enoyl-CoA reductase activity. The inactivation followed a pseudo-first order kinetics and sum of the second order rate constants for the two reductase reactions equaled that for the synthetase reaction. Inactivation of all three activities was prevented by NADPH or its analogs 2',5'-ADP and 2'-AMP but not by the corresponding nucleotides containing the 5'- phosphate. These results suggest that binding of NADPH to fatty acid synthetase involves specific interaction of the 2'-phosphate with the guanidine group of arginine residues at the active site of the two reductases, pH - Dependent inactivation by phenylglyoxal indicated that a group with a pk_a 7.5 is involved in the loss of enzyme activity. Stoichiometric results showed that 4 out of 164 arginine residues per enzyme molecule were essential for the enzyme activity. Page(s): 28-33

Infuence of metal ions on structure and catalytic activity of papain

2012-12-28T16:33:02Z

Title: Infuence of metal ions on structure and catalytic activity of papain Authors: Sathish, H A; Kaul, Purnima; Prakash, V Abstract: Papain is an endoprotease belonging to cysteine protease family. The catalytic activity of papain in presence of two different metal ions namely zinc and cadmium has been investigated. Both the metal ions are potent inhibitors of the enzyme activity in a concentration dependent manner. The enzyme loses 50% of its activity at 2x10^-4 M of CdCI₂ and 4x10^-4 M of ZnCI₂. It is completely inactivated above 1x10^-3 M concentration of either ZnCI₂ or CdCI₂. Of the two metal ions zinc with a k_i value of 5x10^-5 M is a more potent inhibitor than cadmium which has a k_i value of 8x10^-5 M. Both the metal ions have higher affinity for active site than the substrate. At concentrations above 1x10^-2 M of metal ions the inhibition is not reversible. Calorimetric studies showed decreased thermal stability of papain upon binding of these metal ions. Far UV circular dichroic spectral data showed only small changes in the β-structure content upon binding of these metal ions. These data are also supported by decrease in the apparent thermal transition temperature of papain by 5°C upon binding of metal ions indicating destabilization of the papain molecule. The mechanism of both partial and complete inactivation of papain in presence of these two metal ions both at lower and higher concentration has been explained. Page(s): 18-27

Phosphate radical induced oxidation of pyrimidine bases in aqueous solution

2012-12-29T16:33:02Z

Title: Phosphate radical induced oxidation of pyrimidine bases in aqueous solution Authors: Kumar, Maram Ravi; Rao, Mundra Thirupathi; Adinarayana, Mundra Abstract: The photooxidation of pyrimidine bases viz .uracil and cytosine in presence of peroxydiphosphate (PDP) in aqueous solution at natural pH (~7.5) has been carried out in a quantum yield reactor using a high-pressure mercury lamp. The rates of oxidation and quantum yields of pyrimidine oxidation have been found to increase with increase in [PDP] while they are independent of [pyrimidine] and light intensity. On the basis of these experimental results, product analysis and existence of isosbestic points a probable mechanism is suggested in which peroxydiphosphate ion on photolysis gives phosphate radical anions which initiates the reaction by adding to C(5) or C(6) of pyrimidine base leading to the formation of pyrimidine radical via radical cation or hydrolysis. This further reacts with PDP and gives the final products 5,6-dihydroxy pyrimidine and isobarbituric acid. Page(s): 13-17

Penicillin acylase catalyzed synthesis of penicillin-G from substrates anchored in cyclodextrins

2012-12-29T16:32:55Z

Title: Penicillin acylase catalyzed synthesis of penicillin-G from substrates anchored in cyclodextrins Authors: Prabhu, K Sandeep; Ramadoss, Candadai S Abstract: Penicillin acylase (EC 3.5.1.11 ) catalyses the condensation of phenylacetic acid (PAA) and 6-aminopenicillanic acid (6-A A) to form benzylpenicillin (BP). Both PAA and 6-APA were found to form host-guest complexes with β-methylcyclodextrin (βm-CD) and γ-cyclodextrin (γ -CD) respectively. The rate of the reaction catalyzed by the enzyme remained unaffected if one of the substrates used was in the cyclodextrin complexed form. However, in this case, the reaction lasted longer and yielded about 20 per cent more products compared to the condensation reaction involving only uncomplexed substrates. There was a distinct increase in the rate of formation of the antibiotic, if both substrates used are in CD-complexed form . Page(s): 6-12