UNISITE CATALYSIS AND THE DELTA-SUBUNIT OF F1-ATPASE IN ESCHERICHIA-COLI

The 5-subunit form of the Escherichia coli F-1-ATPase, characterized b y the subunit composition alpha(3) beta(3) gamma delta epsilon failed to exhibit a rate acceleration when samples of the enzyme hydrolyzing substoichiometric concentrations of [gamma-P-32]ATP were switched from unisite to multisite hydrolysis by the addition of a cold chase. A 4- subunit form of the enzyme lacking in the delta subunit (alpha(3) beta (3) gamma epsilon) did exhibit cold chase-promoted accelerations in th e hydrolysis of ATP. Reconstitution of a 5-subunit enzyme by incubatin g the 4-subunit form of the enzyme with a purified preparation of subu nit delta was accompanied by a disappearance in the response to a cold chase. The rate constants and equilibrium constants for unisite catal ysis by the 4-subunit enzyme did not differ significantly from previou sly reported values that may have been based on a mixture of 4- and 5- subunit forms of the enzyme. The vesicular form of Escherichia coli F, F,-ATPase exhibited a response to a cold chase only if the vesicles we re first extracted with KCl. [gamma-P-32]ATP bound in the high affinit y catalytic sites of KCl-extracted membranes partially dissociated in an energy-dependent manner when the vesicles oxidized NADH.