PHOTOAFFINITY-LABELING OF A CYTOKININ-BINDING INTEGRAL MEMBRANE-PROTEIN IN PLANT-MITOCHONDRIA

Two target polypeptides were detected by photoaffinity labelling of pu rified mung bean mitochondria using tritiated 2-azido-N-6-benzylaminop urine. SDS-PAGE and fluorography of total mitochondrial proteins after the photoaffinity reaction showed a labelled 32 kDa polypeptide (inte nsely labelled) and a 57 kDa polypeptide (less intensely labelled). Th e latter was assumed to be the alpha and/or beta subunit of F(1)ATPase since it was the most abundant polypeptide in gels stained with Cooma ssie Blue. Partial purification of F(1)ATPase demonstrated that the 32 kDa polypeptide was not a component of the ATPase complex. Fractionat ion experiments showed that the 32 kDa protein was integrally associat ed with mitochondrial membranes and could be enriched by simple washin g and detergent extraction procedures.