MEMORY AND IMPRINTING EFFECTS IN MULTIENZYME COMPLEXES .2. KINETICS OF THE BIENZYME COMPLEX FROM CHLAMYDOMONAS-REINHARDTII AND HYSTERETIC ACTIVATION OF CHLOROPLAST OXIDIZED PHOSPHORIBULOKINASE
S. Lebreton et al., MEMORY AND IMPRINTING EFFECTS IN MULTIENZYME COMPLEXES .2. KINETICS OF THE BIENZYME COMPLEX FROM CHLAMYDOMONAS-REINHARDTII AND HYSTERETIC ACTIVATION OF CHLOROPLAST OXIDIZED PHOSPHORIBULOKINASE, European journal of biochemistry, 246(1), 1997, pp. 85-91
Oxidized, free, stable phosphoribulokinase from Chlamydomonas reinhard
tii was almost completely devoid of catalytic activity (0.06 s(-1)/sit
e). However, when it was bound to glyceraldehyde-3-phosphate dehydroge
nase from the same organism, it displayed significant activity (3.25 s
(-1)/site). Moreover, this complex tended to spontaneously dissociate
upon dilution; the isolated phosphoribulokinase activity increased up
to 56 s(-1)/site, subsequently decreased, and finally became almost co
mpletely inactive. Its intrinsic kinetic properties (K-m and k(cat)) c
hanged with the variation of the overall activity. These effects were
paralleled by changes of conformation of the enzyme as revealed by flu
orescence analysis. A model is proposed that allows quantitative expre
ssion of the dynamics of the dissociation of the oxidized bienzyme com
plex and the effects of either of the two substrates, ATP and ribulose
5-phosphate, on this dissociation process. Whereas ATP destabilized t
he complex and promoted its dissociation, ribulose 5-phosphate tended
to stabilize this complex. Inactive, stable, oxidized phosphoribulokin
ase may form a complex with glyceraldehyde-3-phosphate dehydrogenase r
egaining its catalytic activity. In this case, glyceraldehyde-3-phosph
ate dehydrogenase acts in a manner similar, but not identical to a cha
peronin. The information content of the phosphoribulokinase gene, as d
efined by the sequence of its base pairs, was therefore not sufficient
to specify full enzyme activity. It needed the presence of glyceralde
hyde-3-phosphate dehydrogenase to give the oxidized phosphoribulokinas
e a conformation competent for its activity. The potential biological
significance of these effects remains to be discovered.