Lysosomal enzymes in the interphotoreceptor matrix: acid protease

Interphotoreceptor matrix (IPM), washed from the retina and retinal pigment epithelium (PE) of adult bovine eyes, was assayed for acid protease. Considerable enzyme activity was observed in the IPM--close to one-tenth of the total acid protease of the entire retina-IPM-PE functional unit. The specific activity was much higher in that part of the matrix near the PE. Based on the finding of an acid hydrolase in the IPM, the possibility is discussed that PE cells may secrete lysosomal enzymes and that the process of shed-disc digestion may begin in the IPM, prior to phagocytosis by the PE.