Jk. Sainis et N. Jawali, CHANNELING OF THE INTERMEDIATES AND CATALYTIC FACILITATION TO RUBISCOIN A MULTIENZYME COMPLEX OF CALVIN CYCLE ENZYMES, Indian Journal of Biochemistry & Biophysics, 31(4), 1994, pp. 215-220
Calvin cycle multienzyme complex, consisting of phosphoriboisomerase,
phosphoribulokinase and ribulose-1,5-bisphosphate carboxylase (Rubisco
), shows ribose-5-phosphate+ATP dependent CO2 fixation activity with a
small but discernible lag. Transient time analysis showed that the la
g at pH 7 was independent of multienzyme concentration and was signifi
cantly lower than the expected transient time calculated from K-m and
V-max, of the individual enzymes, indicative of channeling of the inte
rmediates in the enzyme complex. Channeling of ribulose-l,5-bisphospha
te was found to offer a catalytic advantage to Rubisco. Rubisco shows
a decrease in activity during catalysis in ribulose-1,5-bisphosphate d
ependent CO2 fixation reaction, due to the formation of the catalytic
inhibitor. Such a decrease of Rubisco activity was not observed in rib
ose-5-phosphate +ATP dependent CO, fixation reaction and the catalytic
inhibitor was also not detected. These results suggested that the int
ermediates are channeled in the complex and channeling offers a cataly
tic facilitation to Rubisco.