Abnormal ornithine carbamoyltransferase in mice having the sparse-fur mutation.

Mice with the X-chromosomal sparse-fur (spf) mutation frequently have urinary bladder stones composed mostly of orotic acid, which was identified by the following criteria: ultraviolet and infrared absorption, spectra, chromatographic behavior, melting point, and reactivity in a specific color test. This clue led to the discovery that spf-bearing mice have an abnormal form of liver ornithine carbamoyltransferase (carbamoylphosphate:L-ornithine carbamoyltransferase, EC 2.1.3.3). Normal ornithine carbamoyltransferase has maximum activity at pH 7.6-8.0 and 80% of maximum activity at pH 10.0.