Nτ-methylhistidine – An index of the true rate of myofibrillar degradation? An appraisal

The use of N^τ-methylhistidine excretion as an index of myofibrillar protein breakdown is reviewed. It is suggested that several criteria should be considered before the technique can be considered valid and these include (i) there should be no reutilization of His (τMe) during protein synthesis, (ii) there should be little change in the His (τMe) content of the muscle during development, (iii) the metabolism, if any, of the His (τMe) should be minimal, (iv) the diet should contain no His (τMe), (v) there should be no other significant source of His (τMe) in the animal other than myofibrillar protein. Following consideration of these factors and of the data obtained using the technique, it is concluded that, with caution, it can be considered a valuable tool in the study of myofibrillar protein breakdown.