Ornithine, Citrulline, and Arginine Metabolism in Watermelon Seedlings.

Abstract

The interconversion of ornithine, citrulline, arginine, other amino acids, and urea in seedlings of watermelon was observed using isotopically labeled intermediates provided by infiltration or added to homogenates. The rapid conversion of arginine, ornithine, and citrulline was observed. Urea is formed from arginine and is further hydrolyzed to CO2 and ammonia. The infiltration of urea C14 results in the incorporation of isotopic carbon in these amino acids and in others. The appearance of the isotope in ornithine, citrulline, and arginine is interpreted to be as a result of CO2 fixation rather than due to a reversal of the arginase reaction. The ready formation of proline from ornithine and arginine, both by intact seedlings and with homogenates, is reported.