Microdetermination of aldose and aldehyde reductases from human tissues

Microfluorometric method has been described for the determination of aldose reductase and aldehyde reductase II activities in human erythrocyte, brain, and lens. The enzyme activity determined by the microfluorometric method was compared with the activity determined spectrophotometrically by following the oxidation of NADPH and fluorometrically by the formation of sorbitol. The activity of aldose reductase in homogenous preparations from human lens, brain, and erythrocyte was identical when determined by NADPH oxidation, NADP formation, and sorbitol formation using glucose as substrate and NADPH as co-factor. This indicated that NADPH oxidation by aldose reductase is not due to a non-specific oxidation by oxidants generated as a result of interaction of aldose reductase and glucose. Similarly, the activity of aldehyde reductase II obtained by NADPH oxidation and that by NADP formation were in good agreement. The microfluorescent method is convenient and accurate and can be used for the determination of aldose reductase in human tissues using glucose as substrate even when the sample size is small.