HYSTERETIC PROPERTIES OF SOLUBLE F-1 ATPASE FROM ESCHERICHIA-COLI .2. NUCLEOTIDE EFFECTS ON THE SLOW CHANGES OF THE ENZYME KINETIC-BEHAVIOR

In a previous paper from this laboratory it was shown that EC.F1 ATPase exhibits a temperature dependent transition between two stable states, called L (low activity) and H (high activity). They differ three-fold in specific activity. I report here the effects of ADP and ATP on this transition. Both nucleotides were found to shift the equilibrium between the two states in the direction of the L state. Further, the velocity of conversion from one state to the other was accelerated by the presence of the nucleotides. It was shown that the two states of the enzyme exhibit different kinetic properties in that: (i) the L state gives a hyperbolic curve when specific activity is plotted against substrate concentration, and ADP produces an immediate competitive inhibition and (ii) the H state exhibits negative cooperativity when such a curve is plotted, and shows a delayed competitive inhibition by ADP. Furthermore, when enzyme in the H state is loaded with ATP its complex kinetic behavior disappears; ADP does not have this effect. The data are interpreted to mean that the H state depleted of ATP may act as an enzyme bearing two alternative catalytic sites. © 1979.