SUMMARY We previously established that xylulose inhibits the growth of the green alga Chlorococcum echinozygotum. Utilizing experiments involving exposure of the alga to NaHC14O3, it was possible to show by counting the C14 activity of methanolic extracts of the algal cells that xylulose inhibited CO2 uptake. Subsequently it was shown that xylulose does not inhibit or otherwise influence the Hill reaction in this alga. Several enzymes related to xylulose metabolism were investigated. It was found that xylulokinase was active in C. echinozygotum while phosphoketolase activity was absent. Transketolase was present but its activity was not notably affected by xylulose. Crude carboxydismutase preparations were found to be inhibited by xylulose and xylulose 5‐phosphate. However, as carboxydismutase was purified further, this inhibition was relatively less. When xylulose 1,5‐diphosphate was prepared synthetically, this compound was found to be the most effective inhibitor of purified algal carboxydismutase. We conclude that d‐xylulose enters the cells of C. echinozygotum where it is converted to d‐xylulose 1,5‐diphosphate which acts as a competitive inhibitor of carboxydismutase.
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Wu et al. (1970) studied this question.