The components of an α-glycerophosphate cycle and their relation to oxidative metabolism in the lens

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Abstract
The concentration of ATP in a lens brei is maintained when the brei is incubated in O2 with [alpha]-glycerophosphate. Lack of [alpha]-glycerophosphate or incubation in nitrogen causes the concentration to decrease. [alpha]-Glycerophosphate has some effect under anaerobic conditions but this is not sufficient to account for the maintenance in oxygen. Manometric experiments show that [alpha]-glycerophosphate enhances the respiration of lens preparations. This respiration can be further increased by the addition of ADP and is abolished by cyanide and an-timycin. The inference from these experiments is that a mitochondrial system able to oxidize [alpha]-glycerophosphate is present, i.e. the particu-late half of the [alpha]-glycerophosphate cycle. More than the calculated proportion of NADH is used when limiting amounts of dihydroxyacetone phosphate are added to lens tissue in spectrophotometric experiments. Dihydroxyacetone phosphate is therefore regenerated and an [alpha]-glycerophosphate cycle is operative. A preparation of a participate [alpha]-glycerophosphate dehydrogenase that takes up O2 with methylene blue as electron acceptor is described. Methods for obtaining mitochondria from lens are compared, and a useful extraction medium is defined. Mitochondria with activities of the same order of magnitude as those obtained from liver, with [alpha]-glycerophosphate and glutamate as substrates, are prepared from epithelium detached from the capsule; some respiratory control is observed.