Biological oxidations in the succinic acid series

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Abstract
There is quantitative evidence that the normal course of biological oxidation of succinate proceeds largely, if not entirely, through fumarate and /-malate. The evidence results from: a comparative study of the oxidations of fumarate and Z-malate in presence of various organisms and tissues; a comparison of the action of malonate and of oxalate on the oxidation of fumarate and Z-malate; and measurements of /-malic acid formed from succinic acid, the observed and calculated quantities being in close agreement. Fumarate and /-malate inhibit the oxidation of succinate in presence of various bacteria and of muscle and brain tissues. The strict aerobes B. alkaligenes, B. subtilis and M. lysodeik-ticus, and also muscle tissue, attack /-aspartate in a different manner from the facultative anaerobes B. coli, B. proteus and B. acidi lactici. The latter oxidize the acid through fumaric and /-malic acids. Malonate not only inhibits the oxidation of succinate by bacteria but also that by muscle and brain tissues, the degree of inhibition being greatest with these tissues. The wide variation with different cells in the degrees of inhibition by malonate is associated with differences between velocities of oxidation of fumarate and those of succinate. Neither malonate nor oxalate inhibits the velocity of oxidation of p-phenylenediamine by brain tissue. These results are discussed in relation to Warburg''s views on the "respiration enzyme" of the cell.