Aspartate transcarbamylase and

The examples given in the preceding pages have demonstrated that zinc in metalloenzymes may have catalytic, regulatory or structural functions. In addition there are some cases where the zinc appears to have no obvious function. Its most common role is that of catalysis, while a structural role has been demonstrated conclusively in only two cases, aspartate transcarbamylase and B. subtilis a-amylase. 

Reactions 3 and 4 indicate that with aspartic acid, aspartic transcarbamylase, and carbamyl-P or acetyl-P, either carbamyl aspartate or acetyl aspartate can be formed. Carbamyl aspartate is the first intermediate in the formation of pyrimidines, and acetyl aspartate, of unknown function, is the amino acid derivative present in the largest concentration in brain of most species (43). 

Nowlan, S. F., and Kantrowitz, E. R. (1985). Superproduction and Rapid Purification of Escherichia coli Aspartate Transcarbamylase and Its Catalytic Subunit under Extreme Derepression of the Pyrimidine Pathway. J Biol Chem 260 14712. 

Figure 1-8. Typical co-ordination complexes of transition metal ions in proteins. 1 M may be Fe2+, as in rubredoxin, or Zn2 as in aspartate transcarbamylase and alcohol dehydrogenase, 2 carboxypeptidase A, 3 carbonic anhydrase, 4 liver alcohol dehydrogenase, 5 azurin, 6 heme group, L is His and L either His or Met in cytochromes, 7 deoxy-heme group in hemoglobin and myoglobin, 8 oxyform of 7, 9 superoxide dismutase.

V. J. Licata and N. M. Allewell. Functionally linked hydration changes in escherichia coli aspartate transcarbamylase and its catal54ic subunit. Biochemistry, 36(333 10161-10167,1997. 

The intramitochondrial location of the arginine-specific carbamyl phosphate synthetase in N. crassa has the additional advantage of assuring separate pools of carbamyl phosphate for arginine and pyrimidine biosynthesis (41). Since this precludes the utilization of carbamyl phosphate produced in the course of arginine biosynthesis by aspartate transcarbamylase and of the pyrimidine-specific carbamyl phosphate by ornithine transcarbamylase, the control of these reac-... 

H23 Herrmann, E. C., Dunn, J. H. and Schmidt, R. R. DEAE paper chromatography to separate intermediates of the pyrimidine biosynthetic pathway and to assay aspartate transcarbamylase and dihydroorotase activities. Analyt. Biochem., 53, 478-483 (1973)... 

Possible hypotheses for the defect in E.v.d.B. are 1. Decreased reutilisation of uracil at the level of uridine phosphorylase or uridine kinase. At low uracil levels reutilisation will predominate over catabolism via the diHPyDH reaction and at high uracil concentrations the reverse will be the case presumably. 2. Increased synthesis of pyrimidines due to a fluctuating regulation at the level of aspartate transcarbamylase and/or ornithine trans-carbamylase. It has to be presumed that attacks of periodic hyperammonemia have not occurred during the limited time of investigations, with the phenomena of patient A.G. in mind. 

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