PAH and pulmonary arterial hypertension: Immunodetection by Western blot of the PAH protein (p.R261-PAH and WT-PAH, for the mutant and WT proteins, respectively) in liver lysates showed the typical 51-kDa PAH band for WT mice, and two PAH bands at 51- and 56-kDa for the heterozygous PahR261Q/WT and homozygous PahR261Q/R261Q (Pah-R261Q) mutant mice (Fig. 3a).