Protein synthesis during photosynthesis

Abstract

Kinetic studies have been performed on the appearance of 14C in free amino acid pools and in the amino acid moieties of protein in Chlorella pyrenoidosa during steady-state photosynthesis with 14CO 2. At the same time, we have determined the total concentrations of free and bound amino acids, permitting us to calculate the specific radioactivity of the free and bound pools of certain primary amino acids. Comparison of the specific activities of the free amino acids pools with the rate of 14C-labeling of the corresponding pools of bound amino acids shows that there is a direct kinetic precursor-product relationship between the actively-turning-over pools of free amino acids and the bound amino acids in the protein. In the case of certain amino acids, notably glycine, the actively-turning-over pool of free amino acid is very small, leading to “saturation” when the average specific activity of the entire free amino acid pool of glycine is only 0.015. The total rate of labeling with 14C of the bound amino acids in protein appears to account for only a fraction of the steady-state rate of labeling of the free amino acid pools. Explanations are offered for the apparent discrepany.