SEPARATION OF THE RESTING AND ACTIVITY OXYGEN CONSUMPTIONS OF FROG MUSCLE BY MEANS OF SODIUM AZIDE

Abstract

Sodium azide (NaN3) exerts no immediate inhibitory effect on the O2 uptake of resting frog muscle over a conc. range from 10-5 to 10-1 M, and a pH range from 7.4 to 4.0. In contrast the increment in respiration caused by electrical or chemical stimulation or subcontracture doses of caffeine is completely eliminated within a few minutes by 0.002 to 0.005 M azide even at pH 7.4. Higher concs. cause no further decrease in rate below the resting level. The . oxidation of p-phenylene diamine is almost completely inhibited, but the increased O2 consumption due to the addition of carriers such as methylene blue and phycocyanin is not prevented by this poison. Cyanide inhibits both the resting and activity O2 consumptions but with sufficiently different kinetics to indicate that the action may be on different enzyme systems. The results cannot be explained on the basis of "unsaturation" of the enzyme surfaces and it is concluded that the respiration of frog muscle can be separated into 2 qualitatively distinct fractions. Only the activity respiration traverses the cytochrome-cyto-chrome oxidase system.