title: Study on the role of SH-groups in the activity of muscle pyruvate dehydrogenase.
abstract: The kinetics of inactivation of the pyruvate dehydrogenase component of the pigeon breast muscle pyruvate dehydrogenase complex in the presence of 5,5'-dithiobis (2-nitrobenzoate) is biphasic. The rate constants for the fast and slow phases of the inactivation reaction are close to those for modification of two classes of SH-groups differing in their reactivities towards the inhibitor. The reaction order with respect to the inhibitor concentration suggests that the two distinct SH-groups are essential for the enzyme activity. Modification of these SH-groups results in inhibition of the overall activity of the pyruvate dehydrogenase complex and of the 2-hydroxyethyl thiamine pyrophosphate - acceptor oxidoreductase activity of its decarboxylating component. Thiamine pyrophosphate exerts a protective effect on the enzyme only at the slow phase of the enzyme inactivation and SH-modification. As a result of interaction between the holoenzyme and pyruvate (or apoenzyme and 2-hydroxyethyl thiamine pyrophosphate) the rate of the enzyme inactivation is increased. This is associated with masking of non-essential SH-groups and with an increase of the accessibility of two essential SH-groups to the inhibitor. The data obtained suggest the interrelationship between the essential SH-groups and the 2-hydroxyethyl thiamine pyrophosphate-acceptor oxidoreductase activity of pyruvate dehydrogenase.
mesh_terms: D015086:2,6-Dichloroindophenol / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D010856:Columbidae; D004228:Dithionitrobenzoic Acid / Q000494:pharmacology*; D007700:Kinetics; D009132:Muscles / Q000201:enzymology*; D009579:Nitrobenzoates / Q000494:pharmacology*; D011768:Pyruvate Dehydrogenase Complex / Q000378:metabolism*; D013438:Sulfhydryl Compounds / Q000032:analysis; D013835:Thiamine Pyrophosphate / Q000494:pharmacology
chemical_list: D009579:Nitrobenzoates; D011768:Pyruvate Dehydrogenase Complex; D013438:Sulfhydryl Compounds; D004228:Dithionitrobenzoic Acid; D015086:2,6-Dichloroindophenol; D013835:Thiamine Pyrophosphate