Sex- and phenotype-dependent metabolism of N tau-methylhistidine by mice.

The metabolism of N tau-Me-14C]methylhistidine by mice was influenced by both the sex and the phenotype of the animal. After subcutaneous injection of labelled N tau-methylhistidine, recoveries of radioactivity in excreta were incomplete, and the distributions of radioactivity showed that different mouse phenotypes degraded N tau-methylhistidine in vivo to different extents. Hence the excretion of N tau-methylhistidine by mice cannot be used as an index of protein breakdown in vivo.