Uptake of NADPH by islet secretion granule membranes.

Reduced nicotinamide adenine dinucleotide phosphate (NADPH), which stimulated the release of insulin from toadfish islet cells and from isolated secretion granules, was taken up by the membranes prepare from these secretion granules. Oxidized nicotinamide adenine dinucleotide phosphate, which did not release insulin from the granules, was taken up to a much lesser extent. The uptake of NADPH by the granule membranes was time dependent, reaching equilibrium in about 30 min. The maximum amount of NADPH taken up was 0.6 nmol/mg membrane protein and the concentration of NADPH needed to obtain maximum uptake was 6.5 x 10(-4)m, which was approximately the same concentration of NADPH needed to produce maximum release of insulin from the secretion granules.