T. Hisabori et K. Mochizuki, MAGNESIUM REGULATES BOTH THE NUCLEOTIDE-BINDING AND THE ENZYME-ACTIVITY OF ISOLATED CHLOROPLAST COUPLING FACTOR-1, Journal of Biochemistry, 114(6), 1993, pp. 808-812
The inactivation and the activation of the ATPase of isolated CF1 as a
ssayed by the hydrolysis of ATP in 10 s depended on prior binding of A
DP-Mg and ATP-Mg. The effects of Mg2+ on the nucleotide binding kineti
cs were studied by monitoring the time courses of UV spectral changes
induced by the interaction between CF1 and ADP or ATP using a rapid-sc
an spectrophotometer equipped with a stopped-flow cell. The apparent r
ate constant of ADP binding to the two high-affinity sites on CF1 (des
ignated sites B and C in the previous report [Hisabori, T. and Sakurai
, H. (1984) Plant Cell Physiol. 25, 483-493]) was drastically increase
d by prior binding of Mg2+ to CF1, but not ATP. The inhibitory effect
of Mg2+ was attributed to a marked increase in k(on), for the inhibito
ry ADP binding at the high-affinity sites induced by the previous bind
ing of Mg2+ to the enzyme. The location of site B is suggested to be o
n the beta subunit based on the difference spectral change induced by
binding of the ADP analog 2',3'-O-(2,4,6-trinitrophenyl)ADP to CF1.