Abstract
1. 1. The complete enzyme sequence of de novo pyrimidine biosynthesis has been found in crude extracts of Plasmodium berghei. 2. 2. Carbamoylphosphate synthase (CPS'ase) utilises l-glutamine and not ammonia as the amine group donor. 3. 3. Aspartate transcarbamoylase (ATC'ase) activity was maximal at pH 9.1 and exhibited normal Michaelis-Menten kinetics with both substrates; apparent K m s were 0.47 mM for Carbamoylphosphate and 2.38 mM for l-aspartate. 4. 4. No purine or pyrimidine metabolite was found to affect the activity of ATC'ase. 5. 5. A range of dicarboxylic acids and a proposed analogue of the transition state, N-( Phosphonacetyl)- l-aspartate (PALA) were found to be inhibitory. The inhibition constant for PALA was 0.48 μM. 6. 6. CPS'ase and ATC'ase both elute in the void volume of Agarose A-5 M and Sephadex G-200 gel columns.
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