CHANNELING OF THE INTERMEDIATES AND CATALYTIC FACILITATION TO RUBISCOIN A MULTIENZYME COMPLEX OF CALVIN CYCLE ENZYMES

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.