A particulate cytoplasmic fraction enhancing photosynthesis of isolated pea chloroplasts. I. Kinetic aspects and some characteristics of the phenomenon

A particulate cytoplasmic fraction was found capable of enhancing CO₃fixation, accompanied by CO₂-dependent O₂evolution, in isolated chloroplasts obtained from pea seedlings (Pisum sativum L. cv. Dan). Carbon dioxide fixation by chloroplasts obtained from seedlings kept in the dark for 24 h prior to extraction could be enhanced up to 300%, while the photosynthetic rate of chloroplasts from pre-illuminated seedlings was enhanced only by 50%. The enhancement of photosynthetic capacity of the isolated chloroplasts persisted at maximal rates for a longer time than that of isolated chloroplasts without addition of the cytoplasmic fraction. This enhancement was light dependent. The particulate cytoplasmic fraction by itself did not fix CO₂but did consume oxygen. The enhancement was not the result of chloroplast fragments being present in the particulate fraction.