Glucose-6-phosphate dehydrogenase is present in lettuce seeds and seedlings in a particulate, 20,000gfraction and in a soluble fraction of the cells. In both fractions the enzyme activity occurs in the presence of either NAD or NADP. It seems probable that an enzyme with two active sites is involved.Total activity does not change during 48 hours germination in water. It is depressed by coumarin or thiourea treatment. Specific activity rises in the soluble fraction when germination occurs, but not in the mitochondrial one. Coumarin treatment largely depresses the increase in specific activity. In vitro 100 ppm coumarin totally inhibit enzyme activity. 1,250 ppm thiourea do not affect enzyme activity.The results are analysed and it is concluded that glucose-6-phosphate dehydrogenase is important, if at all, only in the very early stages of germination.
展开▼
