Photochemical activation of Rana pipiens tyrosinase

Molecular cloning and biochemical characterization of the skin tyrosinase from Rana esculenta L.

“…One of the most intriguing properties of the amphibian tyrosinases is their occurrence as inactive forms in crude skin extracts, that require treatments such as limited proteolysis or others to become fully active (Barisas and McGuire, 1974;Chen, 1975;Lozano et al, 1975;Mikkelsen and Triplett, 1975a;Mikkelsen et al, 1975b;Peñafiel et al, 1982;Wittenberg and Triplett, 1985a,b). Functional expression of the cloned R. esculenta tyrosinase gene allowed us to gain insight into this phenomenon.…”

Subunit interactions in tyrosinase from frog epidermis in immobilized enzyme systems

“…Although several studies have demonstrated that frog epidermis tyrosinase is a tetrameric enzyme composed of identical subunits (Barisas & McGuire, 1974;Mikkelsen & Triplett, 1975), none has attempted to assess the possible catalytic activity of subunits. The results reported in the present paper, together with the cross-linking experiments performed to study the determination of quaternary structure of tyrosinase (J. L. Iborra, J.…”

“…The two types of activity are referred to as hydroxylase and oxidase respectively. Amphibian epidermal tyrosinase is extracted in the proenzyme form and is easily activated by proteinases (McGuire, 1970), light (Mikkelsen et al, 1975), heat (Chen, 1975) and immobilization on a solid support (Iborra et al, 1979). Frog epidermis tyrosinase of Rana pipiens seems to have a tetrameric structure in both active and inactive forms of the enzyme (Barisas & McGuire, 1974;Mikkelsen & Triplett, 1975).…”

“…Amphibian epidermal tyrosinase is extracted in the proenzyme form and is easily activated by proteinases (McGuire, 1970), light (Mikkelsen et al, 1975), heat (Chen, 1975) and immobilization on a solid support (Iborra et al, 1979). Frog epidermis tyrosinase of Rana pipiens seems to have a tetrameric structure in both active and inactive forms of the enzyme (Barisas & McGuire, 1974;Mikkelsen & Triplett, 1975). From the results of cross-linking experiments, we have established that tyrosinase from frog epidermis of Rana esculenta ridibunda is formed from four identical or similar subunits, and the existence of an association-dissociation equilibrium between them (J.…”

Some properties ofBufo bufo tyrosinase during development

“…Different methods 9 were employed to prepare melanized 'late' melanosomes ( fig. In fact, premelanosomes from the stage 8 and late melanosomes from the stages 3, 6,9,12,14 show no spectrophotometrically detectable activity but the same electrophoretic tyrosinase band; starting from stage 19 enzyme activity from late melanosomes dramatically increases but the electrophoretic band of tyrosinase is the same as in previous stages. The negatively stained melanosome preparations for the electron microscopy were prepared as previously described 9.…”