Summary1. In liver and brain there are two distinct mechanisms for phosphorylation, which may be separated by centrifligation of the tissue homogenates: (1) particulate elements dependent on oxidation of succinate or other substrates of the tricarboxylic acid cycle and (2) water-soluble or at least water-borne systems glycolyzing hexose diphosphate. In the Walker 256 tumor the major part of the phosphorylating effect appears to be induced by the water-soluble, hexose diphosphate glycolyzing system, which functions equally well under aerobic and anaerobic conditions. 2. While the oxidative phosphorylation carried out by liver and brain particles with succinate or a-ketoglutarate is readily blocked by extremely dilute solutions of dini-troeresol, the water-borne, glycolytic, phosphorylating system which' passes into the supernate on centrifuging the homogenate is not suppressed by dinitrocresol, even when used at concentrations from 100- to 500-fold those which completely suppress aerobic phosphorylation of...