The Relation of Glucose Absorption to Respiration in Potato Slices

Abstract

While the gross respiration rate of potato disks increases approximately threefold in a day, glucose utilization as measured by the production of C14O2 from uniformly labeled glucose increases more than 3,000 times. In normally aged disks, which suffer a 50-60% inhibition of the total respiration by malonate and an inhibition of less than 10% by cyanide, C14O2 evolution is almost totally suppressed by either inhibitor. When disks are aged in a manner which leads to a fully malonate-resistant respiration as measured by oxygen consumption, C14O2 production is also malonate resistant. Glucose absorption by normally aged disks is inhibited both by malonate and by cyanide, but not by uncouplers of oxidative phosphorylation. Glucose absorption is unaffected by malonate in tissue wherein respiration is malonate-resistant. In general, glucose absorption and C14O2 production are constant with time as the ambient glucose concentration drops. The observations taken together suggest that glucose uptake is carrier-mediated by a system similar to that in human red cells which leads to equilibrium exchange without accumulation. The cytoplasmic glucose concentration is deemed to control glucose absorption, and the developed, or induced respiration is presumed to determine the cytoplasmic glucose concentration. It is tentatively proposed that malonate resistance reflects a metabolic path indifferent to malonate, while cyanide resistance represents compensation by a new or altered respiratory system when the normally sensitive respiration is inhibited by cyanide.