Endocrinology, Vol 129, 1370-1374, Copyright © 1991 by Endocrine Society

ARTICLES

Quinone reductase enzyme activity in pancreatic islets

MJ MacDonald
Childrens Diabetes Center, University of Wisconsin Medical School, Madison 53706.

A water-soluble quinone, coenzyme Q0 (CoQ0), was shown to stimulate insulin release, and dicumarol, an inhibitor of quinone reductase, inhibited glucose-induced insulin release in pancreatic islets. Since this suggested that quinone reductase might play some role in physiological insulin release, this enzyme was characterized in islets. More than 90% of the total activity was located in the cytosol, but the specific enzyme activity was highest in the microsomal fraction. The relative rates of activity with various substrates (CoQ0 approximately equal to durohydroquinone greater than menadione greater than duroquinone greater than CoQ6 = CoQ10 greater than ferricyanide) were similar to those described previously for quinone reductase from liver Dicumarol, chlorpromazine, and T3 were much more potent inhibitors of the enzyme when NADPH was the coenzyme than when NADH was the coenzyme. Dicumarol was the most potent inhibitor. The enzyme was not inhibited by rotenone. Islets ranked second to liver in quinone reductase activity, but the activity in islets was much closer to that found in all other tissues examined. Quinone reductase may play a role in insulin secretion.

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