The metabolism of labetalol in animals and man.

dehydrogenases. NAD+ and NADP+ are reducible at the dropping mercury electrode, and the cathodic waves may be measured in the region -1.1 V to -1.3 V. The reduced nucleotides NADH and NADPH are not electroactive at these potentials and thus do not interfere with themeasurements. Under somecircumstances, this polarographic assay for a dehydrogenase may offer advantages over the conventional spectrophotometric method. Such situations include the presence of turbid suspensions, e.g. in the examination of enzyme activities in cells made permeable (Weitzman, 1973), and the presence of NADH oxidase activity. The latter interferes with the normal assay for dehydrogenases, but, under the anaerobic conditions used in polarographic measurements, is inoperative. The enzymes measurable by the polarographic procedure may also, of course, serve as coupling enzymes and thereby extend the method to other reactions and the general approach to polarographic assays outlined here should prove applicable to many other enzymes. The ability of polarographs to measure very small currents renders these assay methods comparable in sensitivity with other available (generally spectrophotometric) procedures. In conclusion, a number of enzyme activities may be determined polarographically. The method is continuous and sensitive, may be performed under a wide range of experimental conditions and is unaffected by solution turbidity. In particular cases, additional advantages may be presented.