Asparagine Biosynthesis by Cotton Roots

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 CO2 fixation. Whereas short term 14CO2 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 14CO2 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 14CN− are β-cyanoalanine and asparagine. Similarly to CO2 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.