Importance of SH-groups for enzymic activity: studies on lactic acid dehydrogenase in hog heart
Pfleiderer, G.; Jeckel, D.; Wieland, T.
Archives of Biochemistry and Biophysics 83(1): 275-282
ISSN/ISBN: 0003-9861 PMID: 13662015 DOI: 10.1016/0003-9861(59)90033-5
Lactic acid dehydrogenases (LDH) from pig heart and rat- or rabbit skeletal muscle contain 14 Sh groups, as has been determined by spectrophotometry after reaction with PC1MB, N-ethylmaleimide, quinone and as cysteic acid. In the native Ldh from pig heart only 3 Sh groups react rapidly with the mercurial, after denaturation by urea all Sh groups become reactive. The enzyme, after poisoning with 3 equ. of PC1Mb is fully restored by glutathione. The reactivated Ldh adsorbs only 2 moles of DPN-sulfite. It seems, therefore, that only 2 Sh groups are necessary for whole enzymatic activity. p-Benzoquinone has been used as stoichiometric Sh blocking agent. The number of quinone molecules bound to the protein can be determined spectrophotometrically at 440 mμ. Dpn and l-lactate protect Ldh against denaturation by urea, preventing unfolding of the protein structure.