ИСТИНА

When MgADP without phosphate is bound at a catalytic site of H+-FoF1 ATP synthase, there is a probability that the enzyme gets blocked in an inacitive conformation. This phenomenon is known as MgADP inhibition. Earlier experiments indicate that the enzyme adopts a special inactive conformation with MgADP trapped in a catalytic site. This is a core feature of ATP synthase observed even in the minimal catalytic alpha3beta3gamma-complex. MgADP inhibition is found in all ATP synthases studied so far. However, the degree of inhibition varies considerably, being strong in mitochondria and especially chloroplast enzyme, as well as in some bacteria, e.g. Bacillus PS3, but rather weak in FoF1 from Escherichia coli. We have demonstrated previously that in Bacillus PS3 ATP synthase mutation betaGln259Leu can dramatically decrease MgADP inhibition. In E.coli wild type enzyme the residue in the corresponding position (beta249) is Leu, i.e. it is similar to the mutant Bacillus PS3 enzyme. In this work we made an E.coli mutant betaLeu249Gln. The mutation significantly enhanced MgADP inhibition. Moreover, it completely changed the effect of phosphate on MgADP inhibition: while in the wild-type enzyme phophate increased the inhibitory effect of MgADP, in the betaLeu249Gln it releived the inhibition. We conclude that MgADP inhibition is a relatively easily modulated regulatory feature of ATP synthase rather than an inevitable "side effect" of the rotary catalytic mechanism.