On the acceptor specificity of glycollate oxidase of Nicotiana tabacum

Abstract

The effect of compounds on the activity of ammonium sulphate preparations of glycollate oxidase from Nicotiana tabacum cv. John Williams' Broadleaf and the aurea mutant Su/su is reported. Coupling to DCPIP as terminal oxidant under anaerobic conditions gave greater rates of glycollate oxidation than when measured as O₂ uptake in the presence of cyanide. The enzyme also linked to DCPIP in the presence of O₂, showing that it is a facultative aerobic dehydrogenase. Catalytic amounts of PMS stimulated enzyme-dependent oxygen uptake and DCPIP reduction under aerobic and anaerobic conditions. This further suggests that an intermediate carrier, or alternate acceptor, depending on concentration, exists before O₂ in vivo. Naturally occurring quinoid compounds may fulfill such a role, as evidenced by the enhancement of aerobic DCPIP reduction upon addition of catalytic amounts of caffeic and chlorogenic acid. The observation that PMS, caffeic and chlorogenic acid, biopterin, 6-hydroxy-2-amino-4-hydroxypteridine and a quinone extract of N. tabacum quenched the inhibitory effect of blue light on tobacco glycollate oxidase, is in accordance with the possible function of such compounds in glycollate oxidation.