Peroxidase and Tyrosinase Are Present in Secondary Lysosomes That Degrade Photosensory Membranes of the Crayfish Photoreceptor: Possible Role in Pigment Granule Formation

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Abstract
Three enzymes (acid phosphatase, peroxidase, and tyrosinase) were localized by electron microscopy within the retina of crayfish Orconectes limosus. Peroxidase activity was observed only in lamellar bodies, which are secondary lysosomes and degrade photosensory membrane. After H2O2 was omitted from the reaction medium, peroxidase activity in lamellar bodies was partly inhibited but was not missing completely. After addition of sodium pyruvate, which inhibits endogenous generation of H2O2, staining of lamellar bodies was absent. Tyrosinase activity was found in lamellar bodies and in small vesicles within the rhabdoms similar to those found positive for acid phosphatase. Granules (500–700 nm in diameter) with an electron opaque matrix and mature screening pigment granules showed tyrosinase activity. Moreover, lamellar structures within membrane‐bound organelles that additionally contained screening pigment‐like granules were electron dense because of tyrosinase activity. After addition of phenylthiourea (PTU) to the incubation medium, lamellar bodies did not generally contain electron dense deposits, although weak staining of single membranes still was sometimes observed. After addition of sodium pyruvate in combination with PTU, no staining was detected. The possible role of tyrosinase in ommochrome synthesis within secondary lysosomes that degrade photosensory membrane is discussed.