CROSS-LINKING 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 (α: Mr 53 906; β: 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 α2, αβ and β2, and the trimer α2β were obtained. A small amount of tetramer, probably α2β2, 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. © 1990.