Decreased structure-linked latency of lysosomal dipeptidyl aminopeptidase-I activity in Duchenne muscular dystrophy fibroblasts

Crude lysosomal pellets were prepared from skin fibroblasts grown from patients having Duchenne muscular dystrophy, and from normal controls. Disruption of the lysosomes by nonionic detergents resulted in the expression of latent activity of the enzyme dipeptidyl aminopeptidase-I(DAP-I). Duchenne lysosomes showed less structure-linked latency than those from normal controls, and sedimentation studies demonstrated that the difference was not caused by increased leakage of the enzyme from lysosomes. Permeability properties of the lysosomes for an artificial substrate revealed no difference of the apparent Km. However, in intact lysosomes the apparent KR for C1 of this chloride-requiring enzyme was found to be lower in DMD lysosomes. The apparent increase in entry of C1 was closely related with the decreased amount of the DAP-I latency. High concentrations of extra-lysosomal C1- corrected the abnormality.