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CHLOROPLAST STRUCTURE AND FUNCTION IN ac-20, A MUTANT STRAIN OF CHLAMYDOMONAS REINHARDI : I. CO₂ Fixation and Ribulose-1,5-Diphosphate Carboxylase Synthesis

R. K. Togasaki ¹ and R. P. Levine ¹

¹ From The Biological Laboratories, Harvard University, Cambridge, Massachusetts 02138.

Dr. Togasaki's present address is the Department of Botany, University of Indiana, Bloomington, Indiana 47401

A mutant strain of the green alga Chlamydomonas reinhardi, ac-20, is described in which both the rate of CO₂ fixation by whole cells and the rate of carboxylation of ribulose-1,5-diphosphate in cell-free extracts are reduced, particularly when sodium acetate is present in the growth medium. Of the enzymes of the reductive pentose phosphate cycle tested, only ribulose-1,5-diphosphate carboxylase activity is reduced in the mutant strain, and it appears that the low carboxylase activity limits the strain's rate of photosynthetic carbon metabolism. Evidence is presented to show that the fluctuation in the level of the enzyme activity in the presence or absence of acetate results from the fluctuation in the level of some factor(s) limiting the rate of synthesis of the protein.

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• Inwood, W., Yoshihara, C., Zalpuri, R., Kim, K.-S., Kustu, S. (2008). The Ultrastructure of a Chlamydomonas reinhardtii Mutant Strain Lacking Phytoene Synthase Resembles that of a Colorless Alga. Mol Plant 1: 925-937 [Abstract] [Full Text]  

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