Carbon dioxide fixation by isolated chloroplasts of Euglena gracilis: II. Inhibition of CO2 fixation by AMP

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Abstract

CO2 fixation in isolated Euglena chloroplasts is strongly inhibited by AMP. Adenosine, ADP, and adenine are also inhibitory, but to a lesser extent. Other nucleotide monophosphates including 3′-AMP are not inhibitory and all other purines tested, except those containing a 6-amino group, are ineffective. Euglena chloroplast preparations are found to contain an active adenylate kinase, and it appears that ADP is converted to AMP, which in turn causes the inhibition. AMP does not reduce the rate of photophosphorylation or of NADP photoreduction. Several enzymes of the reductive pentose phosphate cycle are apparently not inhibited by AMP, including 3-phosphoglycerate kinase, NADP-linked glyceraldehyde-3-phosphate dehydrogenase, ribulose-1,5-diphosphate carboxylase, phosphoribulokinase, and ribose-5-phosphate isomerase. Under isotonic conditions there appears to be no interaction between internal and external adenine nucleotides, and the high energy phosphate produced in photophosphorylation cannot be directly transferred to the external adenine nucleotides.

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    This research was supported in part by a grant from the National Institutes of Health to North Carolina State University and by an NDEA fellowship. Contribution from, the Department of Biochemistry, School of Agriculture and Life Sciences and School of Physical and Mathematical Sciences. Paper No. 3626 of the Journal Series of the North Carolina State University Agricultural Experiment Station, Raleigh, NC 27607.

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    Present address: Department of Biochemistry, The University of Texas Medical School, San Antonio, TX.

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