CONSERVATION OF OXIDATIVE ENERGY IN PHOSPHATE-FREE SYSTEMS . FORMATION OF ACYL ANHYDRIDES VIA OXIDATION OF HYDROQUINONE MONOCARBOXYLIC ESTERS

1. The free energy released by the oxidation of hydroquinone monoesters or of 6-hydroxychroman-2-ones, using N-bromosuccinimide in glacial acetic acid as oxidant, is trapped and conserved by the formation of acyl anhydrides. For example, by oxidation of 2-methyl-1,4-naphthohydroquinone-1-acetate, acetic anhydride is formed in at least 98% yield. 2. Such observations with model compounds suggest a cyclic scheme for energy conservation in mitochondria, in which ubihydroquinone is postulated to esterify with a protein carboxyl group (without prior carboxyl activation); the resulting ester is oxidized and a labile acid anhydride (or isoenergetic acyl function) is generated within the protein matrix. Reaction of the acid anhydride with inorganic phosphate and, subsequently, with ADP, provides a pathway for the oxidative generation of ATP, by way of a nonphosphorylated high energy intermediate. 3. That the proposed esterification step is feasible in a protein matrix is supported by the demonstration of a facile and complete conversion of coumarinic acid to coumarin at pH 4. © 1969.