The disintegration of yam tuber gamma-glutamyl transpeptidase during tuber storage.
As an attempt to understand some aspects of the protein catabolism in the resting yam (Dioscorea rotundata) tuber with respect to the storage problems of the tuber, gamma-glutamyl transpeptidase (gamma-GTP) was isolated from healthy tubers after aerobic storage for varying periods. The molecular weight was determined by SDS-gel electrophoresis and the activity by spectrophotometry using gamma-glutamyl alpha-naphthylamide as substrate. Molecular weight and activity were plotted versus duration of the tuber storage. The molecular weight of the gamma-GTP from newly harvested tuber was 2.2 . 10(5). Both the mol. wt and activity decreased linearly with tuber storage, the two processes having approximately equal first order rate constant, 1.2 . 10(-2)/week, with a half-life of 58 weeks. High molecular weight forms of tuber gamma-GTP when dissociated and gel electrophorized gave in each case a lower molecular weight form that also had enzymic activity. A plot of the mol. wt versus the activity gave a straight line which intersected the mol. wt axis at 200000, which is the mol. wt of the smaller subunit of gamma-GTP. These results show that yam tuber gamma-GTP undergoes progressive disintegration during tuber storage and in this process the components are lost probably from the larger subunit after proteolytic cleavage and subsequent dissociation of the cleaved components.
D004355:Drug Stability; D006207:Half-Life; D008970:Molecular Weight; D010944:Plants / Q000201:enzymology*; D013997:Time Factors; D014675:Vegetables; D005723:gamma-Glutamyltransferase / Q000378:metabolism*
D005723:gamma-Glutamyltransferase