Assimilation of ammonia by nitrogen-starved cells of Chlorella vulgaris

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Abstract
A previously observed ammonia-induced rise in uncombined alanine in nitrogen-starved Chlorella was confirmed and extended. Inhibitors such as dinitrophenol and deoxypyridoxine had little effect in altering the alanine increase. Enzymes to provide a direct amination of pyruvate were sought and not found. Glutamic dehydrogenase and glutamic acid-alanine transaminase were present in cell-free Chlorella preparations. The measurement of the N15 content of uncombined alanine, glutamic acid and glutamine after the feeding of N15H4NO3 to Chlorella showed that a direct amination of pyruvate to form ammonia was unlikely and that transamination from glutamic acid to pyruvate was a likely possibility. Although it was observed that an increase in pyruvate was a result of ammonia addition, the external addition of pyruvate exerted only a small effect on alanine content. It was concluded that part of the alanine increase was a result of an ammonia-induced increase in pyruvate and which in turn induced an increase in alanine from the action of glutamic acid-alanine transaminase.