A lysosomal factor that interconverts multiple forms of rat liver tyrosine aminotransferase

A particulate factor of rat liver is described which interconverts three forms of rat liver cytosolic tyrosine aminotransferase in vitro with no alteration of enzyme activity. The factor appears to be a heat- and pH-sensitive lysosomal protein. The interconversion process is stimulated in vitro by 2.5 mM MgCl 2 and 2.5 mM ATP. Asparate aminotransferase multiple forms are also susceptible to in vitro interconversion by the lysosomal factor. The properties of the factor explain several anomalous effects of in vitro manipulation on the tyrosine aminotransferase forms which have been reported in the literature and implicate the form interconversion in the degradation of tyrosine aminotransferase.