title: Molecular origin of the aging effects in glyceraldehyde-3-phosphate dehydrogenase.
abstract: Rat muscle glyceraldehyde-3-phosphate dehydrogenase was reacted with two reagents aimed at the highly reactive cysteine-149 residue in the active site of the enzyme. The enzyme was rapidly inactivated by iodine monochloride. Complete inactivation occurred when approx. 6 mol ICl were added per mol enzyme, indicating that reactions which compete with the reagent's interaction with cysteine-149 take place. Iodine was also found to inactivate the enzyme rapidly and effectively, and, when not in excess, this reagent interacted specifically with cysteine-149. The fraction of original enzymatic activity which could be restored by 2-mercaptoethanol in enzyme samples inhibited by 4.2 mol I2/mol enzyme, decreased with time to a limiting value of 0.6 reached after approx. 15 min. The enzyme thus treated showed a remarkable similarity to enzyme samples purified from old rats, both in its activity and in NAD+ binding patterns under various conditions. It is concluded that the structural modifications induced in the modified enzyme resemble the age-related modifications in native 'old' enzyme. These results demonstrate that the origin of the age-related effects in glyceraldehyde-3-phosphate dehydrogenase is in subtle, post-synthetic structural changes. The inactivation reactions described above require a non-reducing environment for the enzyme. Whether such conditions do exist in cells of old animals is the subject of future studies.
mesh_terms: D000375:Aging; D000818:Animals; D001051:Apoenzymes / Q000378:metabolism; D002712:Chlorides / Q000494:pharmacology; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000378:metabolism*; D007454:Iodides / Q000494:pharmacology; D007700:Kinetics; D024510:Muscle Development; D009132:Muscles / Q000201:enzymology; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D001051:Apoenzymes; D002712:Chlorides; D007454:Iodides; C009813:iodine monochloride; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases