caa a22 4500 39755611X CHVBK 20180308164802.0 cr unu---uuuuu 161202e199606 xx s 000 0 eng 10.1093/oxfordjournals.jbchem.a021366 doi (NATIONALLICENCE)oxford-10.1093/oxfordjournals.jbchem.a021366 Kinetic Characterization of the Endogenous Glutathione Transferase Activity of Octopus Lens S-Crystallin [Elektronische Daten] [Shiao-Shek Tang, Gu-Gang Chang] The kinetic mechanism of the endogenous glutathione transferase (GST) activity of octopus S-crystallin was investigated by steady-state kinetics. Biphasic double-reciprocal plots were obtained for both glutathione and the hydrophobic substrate l-chloro-2,4-dinitro-benzene (CDNB). Substrate inhibition was observed only for CDNB with K5l value of 29.7± 0.01 mM. The catalytic constant for S-crystallin was three orders of magnitude smaller than that for the digestive gland GST of the same species. The initial-velocity studies indicated that the enzyme reaction might conform to a steady-state random Bi-Bi kinetic mechanism, being similar to the reaction of GST from other sources. The pH-rate profiles also suggest that the same chemical mechanism for the nucleophilic aromatic substitution between GSH and CDNB was employed for S-crystallin. The interaction of Tyr7 with the bound GSH lowered the pKa value of the sulfhydryl group of GSH to 6.82-6.85, which is 2.327ndash;2.35 pH unit smaller than that found in aqueous solution. This lowering of pKa, value produces the thiolate anion of GSH, a better nucleophile to attack the ipso carbon of CDNB, resulting in formation of Meisenheimer complex intermediate. Removing the chloride ion from this intermediate complex produces the conjugate product. Using the method devised by Wang and Srivastava (Anal. Biochem. 216, 15-26, 1994), the functional unit of the dimeric S-crystallin was estimated to be a monomer. The possible biological implications of the endogenous detoxification ability of cephalopoda S-crystallin are discussed. © by the Journal of Biochemistry Regular Papers nationallicence enzyme crystallin nationallicence S-crystallin nationallicence glutathione transferase nationallicence kinetics nationallicence cepha-lopods nationallicence Tang Shiao-Shek Graduate Institutes of Life Sciences and Biochemistry, National Defense Medical Center, Taipei, Taiwan aut Chang Gu-Gang Graduate Institutes of Life Sciences and Biochemistry, National Defense Medical Center, Taipei, Taiwan aut The Journal of Biochemistry Oxford University Press 119/6(1996-06), 1182-1188 0021-924X 119:6<1182 1996 119 jbchem https://doi.org/10.1093/oxfordjournals.jbchem.a021366 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1093/oxfordjournals.jbchem.a021366 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Tang Shiao-Shek Graduate Institutes of Life Sciences and Biochemistry, National Defense Medical Center, Taipei, Taiwan aut NATIONALLICENCE 700 1- Chang Gu-Gang Graduate Institutes of Life Sciences and Biochemistry, National Defense Medical Center, Taipei, Taiwan aut NATIONALLICENCE 773 0- The Journal of Biochemistry Oxford University Press 119/6(1996-06), 1182-1188 0021-924X 119:6<1182 1996 119 jbchem Metadata rights reserved CC BY-NC-4.0 http://creativecommons.org/licenses/by-nc/4.0 nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-oxford