Abstract

Abstract It has been shown that, when chloranil is used as electron acceptor in photophosphorylation, phosphorylation has an absolute requirement for molecular oxygen. Although oxygen consumption does proceed in the absence of adenosine diphosphate, the rate of oxygen consumption is doubled in the presence of ADP. The observed P:O and ADP:O ratios at high light intensities are over 3 when chloranil is the acceptor. Under these conditions, the maximum quantum yields at low light intensity for phosphorylation were 0.6, and the quantum yields for electrons (with the use of oxygen as the acceptor) were 1.0. Arguments and data supporting the thesis that chloranil acts only as a noncyclic electron acceptor are given. These high P:O ratios are observed only at low concentrations (approximately 10-8 m) of the oxidized acceptor.

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