Effects of melanin on lysosomal enzymes in bovine ciliary body and iris in vitro

We studied biochemically the effects of melanin on activities of lysosomal enzymes prepared from the bovine ciliary body and iris in vitro. Melanin was prepared from the bovine ciliary body and iris by acid treatment. Acid phosphatase, N-acetyl-beta-D-glucosaminidase, alpha-D-mannosidase, alpha-L-fucosidase, and beta-D-glucuronidase in the ammonium sulfate fraction were used as lysosomal marker enzymes. After the enzyme solution was incubated with melanin, enzyme activity was reduced and protein content in the supernatant was decreased. Each enzyme showed a different activity. The data suggested that 1) the decreased activity may depend on the affinity of lysosomal enzyme protein for melanin and 2) each enzyme may have a different affinity for melanin. These findings were discussed with respect to biochemical interaction between melanin and lysosomal enzymes in the ocular tissue in vivo.