UPTAKE AND ASSIMILATION OF AMINO ACIDS BY PLATYMONAS

¹ Department of Organismic Biology, University of California, Irvine, California 92664

The marine flagellate Platymonas subcordiformis rapidly takes up amino acids at concentrations likely to be found in nature. The relation between velocity of uptake and substrate concentration was determined, and the apparent maximum uptake velocity estimated. Accumulated C¹⁴ amino acids were assimilated into alcohol-insoluble compounds and entered oxidative pathways as shown by detection of evolved C¹⁴O₂. The contribution of the uptake mechanism at an ambient glycine concentration of 1.0 µmole/l. to nitrogen requirement of the cell was found to be roughly 10% for optimal laboratory growth conditions. In nature, where growth conditions are probably less favorable, the contribution would be considerably greater. This provides further support for a normal role of heterotrophy in phytoplankters.

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