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REACTIONS OF O ‐ 2 , H 2 O 2 AND OTHER OXIDANTS WITH SULFHYDRYL ENZYMES‡
Author(s) -
Armstrong David A.,
Buchanan John D.
Publication year - 1978
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1978.tb07011.x
Subject(s) - chemistry , papain , radical , dithiothreitol , catalase , enzyme , superoxide dismutase , stereochemistry , reaction rate constant , oxygen , glutathione , medicinal chemistry , biochemistry , kinetics , organic chemistry , quantum mechanics , physics
Abstract— The inactivation of a number of sulfhydryl enzymes by H 2 O 2 . OH and O ‐ 2 is discussed. and the efficiencies of inactivation for the free radicals are compared with those of halide radicals. The enzymes with essential acyl‐binding SH groups (papain and GAPDH) exhibit a higher sensitivity to inactivation by O ‐ 2 and H 2 O 2 than those with “unactivated” SH groups (LDH and ADH). The sulfenic acid derivatives from the reactions of papain and GAPDH with H 2 O 2 are repairable by RSH molecules, the rates of repair depending on the nature of the R group. Comparisons of rate constants show that competitive scavenging by RSH must be a very important mechanism for the protection of sensitive SH‐containing proteins against OH, and for papain in oxygen‐free solutions the efficiency of this protection increased in the order GSH < PenSH < CysSH < dithiothreitol. On the other hand, catalase and superoxide dismutase are more effective than RSH compounds in rendering protection against H 2 O 2 and O ‐ 2 . In fact in oxygen‐containing systems the effects of RSH are highly complex, because the OH‐ and/or O ‐ 2 ‐initiated chain oxidation of these molecules produces reactive species, which may inactivate essential SH groups. Experiments with papain showed that the yields and nature of the RSH‐derived species depended on the structure of the R group. Also, very large yields of papain Cys 25 SSR were produced from the reactions of the radicals and H 2 O 2 . In effect, it is apparent that under certain conditions the oxidation of “activated” SH groups of important target molecules could become coupled to the OH or O ‐ 2 ‐initiated oxidation of RSH molecules. This should be taken into account in assessing the overall effectiveness of RSH compounds as cellular protectors.