Effect of β-Methylaspartate on Ornithine Cycle Reactions

β-METHYLASPARTATE (β-MA) was identified1 as a product of glutamate metabolism in cell-free extracts of Clostridium tetanomorphum. β-MA is a strong antimeta-bolite toward aspartate: it is an inhibitor of pyrimidine biosynthesis from aspartate2 and of urea synthesis from citrulline + aspartate3. In addition, β-MA seems to have certain interesting metabolic activities: it participates in transamination reactions in rat and rabbit liver and brain4 and in Escherichia coli5, and it may also be a precursor in the de novo synthesis of thimine6.