Asparagine biosynthesis by cotton roots. Carbon dioxide fixation and cyanide incorporation

Abstract

Asparagine is the dominant amino acid in cotton root tips (Acala SJ-1). Two biosynthetic pathways may be operative. First, asparagine is an ultimate product of nonphotosynthetic CO(2) fixation. Whereas short term (14)CO(2) labeling experiments indicate that malate is the predominant product, asparagine appears exponentially and does not appear to be in an active metabolic pool. Other products labeled with (14)CO(2) are citrate, aspartate, and glutamate. No neutral components are labeled. Secondly, asparagine is synthesized via a pathway starting with cyanide. Major amino acid products labeled with (14)CN(-) are beta-cyanoalanine and asparagine. Similarly to CO(2) fixation, asparagine synthesized from cyanide is not in an active metabolic pool. Other products labeled include anion and neutral components. The exact nature of the latter is not known.