ABSTRACT
The endogenous O2 uptake of sea-urchin egg homogenates (Echinus esculentus) was inhibited by malonate, fluoride, iodoacetate, and fluoracetate.
The addition of the tricarboxylic acid cycle intermediates, citrate, a-keto-glutarate, succinate, fumarate, malate, and glutamate stimulated O2 uptake.
The efficiency of the pyruvate-oxidizing mechanism varied in different preparations, but in some, added pyruvate was completely oxidized.
(1)-(3) strongly suggest the presence of a tricarboxylic acid cycle.
Glycogen, glucose and fructose stimulated O2 uptake. The oxidation of fructose was stimulated by DPN and inhibited by fluoride and iodoacetate.
Glucose-1-phosphate, glucose-6-phosphate, fructose-6-phosphate and fruc-tose-i :6 diphosphate stimulated O2 uptake.
Phosphogluconate also stimulated O2 uptake, which suggests that the enzymes of the hexose monophosphate shunt system may be present.
The experiments described in this paper show that the principal pathway by which carbohydrate is broken down is the normal glycolytic one.
