OTC and ornithine carbamoyltransferase deficiency: D140N in E. coli OTC is reported here to show somewhat reduced activity, suggesting that it helps to facilitate catalysis through coupling of its protonation equilibrium to those of first-layer residues; the huOTC missense mutations D175G and D175V in the aligned position have been reported to be associated with late onset OTCD [89] and with OTCD in heterozygous females [88].