Effect of pH on CN-resistant respiratory activity and regulation on Vigna uniguiculata mitochondria

Mitochondria from Vigna unguiculata cv. Vita 5 have a cyanide insensitive a lternative oxidase cross-reacting with a monoclonal antibody raised against the alternative oxidase of Sauromatum guttatum. In the presence of NADH as substrate and dithiothreitol, the CN-resistant respiration of V. unguicula ta intact mitochondria was found to be significantly influenced by assay pH with an optimum value of 6.25. This effect was still observed when nigeric in, known to abolish Delta pH between the matrix and the intermembrane spac e, was present in the reaction medium. This pH effect was shown to be rever sible. Alternative oxidase activation by pyruvate, also appeared to be pH d ependent with an optimum pH value of 7.25. This modulation of the alternati ve oxidase activity by pH has been tentatively attributed to a new protonat ed-deprotonated status of this protein. (C) 2000 Editions scientifiques et medicales Elsevier SAS.