NADP~+ has a weak activity as a hydrogen aoceptor for rabbit muscle glyceralde-hyde-3-phosphate dehydrogenase. The activity observed for NADP~+ was not due toNAD~+ contamination. Furthermore, the possibilities that the observed activity wascaused by the presence of phosphatase, transhydrogenase and nonenzymio hydrogentransfer from NADH to NADP~+ were all excluded. The presence of a NADP~+ -depen-dent enzyme has also been shown to be unlikely. The kinetic parameters were determined under high concentrations ...