Crosslinking and radiation inactivation analysis of the subunit structure of the pyridine nucleotide transhydrogenase of Escherichia coli.

The pyridine nucleotide transhydrogenase of Escherichia coli consists of two types of subunit (alpha: Mr 53,906; beta: Mr 48,667). The purified and membrane-bound enzymes were crosslinked with a series of bifunctional crosslinking agents and by catalyzing the formation of inter-chain disulfides in the presence of cupric 1,10-phenanthrolinate. Crosslinked dimers alpha 2, alpha beta and beta 2, and the trimer alpha 2 beta were obtained. A small amount of tetramer, probably alpha 2 beta 2, was also formed. Radiation inactivation was used to determine the molecular size of the transhydrogenase. The radiation inactivation size (217,000) and chemical crosslinking are consistent with the structure (Mr 205,146) being the oligomer that is responsible for biological activity.