Purification and properties of carbamate kinase from Streptococcus faecalis

Carbamate kinase (ATP:carbamate phosphotransferase, EC 2.7.2.2) has been prepared from an arginine-adapted strain of Streptococcus faecalis. Approximately a 500-fold increase in specific activity of the enzyme was achieved. Certain properties of the purified enzyme were studied.

• 1.

  1. The apparent molecular weight as measured by sedimentation equilibrium appears to be about 46 000.

• 2.

  2. The pH optimum for the formation of carbamyl phosphate from ATP and ammonium carbamate is 8.4.

• 3.

  3. Studies with p-chloromercuribenzoate and silver-tris(hydroxymethyl)aminomethane indicate that sulfhydryl groups are essential for enzyme activity.

• 4.

  4. Michaelis constants estimated for adenosine 5′-triphosphate (in the formation of carbamyl phosphate) and for adenosine 5′-diphosphate in the reverse reaction, carbamyl phosphate degradation, were about the same, 1·10⁻³ M. No such determinations were possible for carbamyl phosphate or ammonium carbonate; when these substrates were studied under comparable conditions non-linear relationships were obtained for Lineweaver-Burk plots.