The process for the activation of frog epidermis pro-tyrosinase

Abstract

1. Purified pro-tyrosinase from epidermis of the frog Rana esculenta ridibunda can be activated in vitro by several proteinases (trypsin, alpha-chymotrypsin, Pronase) and by light. 2. Both pro-tyrosinase and tyrosinase are composed of a single type of subunit having pI 7.2 and approximate molecular weights 68000 and 62000 respectively. A peptide of low molecular weight is released as a consequence of the proteolytic activation. Pro-tyrosinase and tyrosinase have different quaternary structures, the proenzyme being a dimer of Mr approx. 115000 and the enzyme a tetramer of Mr approx. 210 000. 3. The activation process was affected by several agents (L-3,4-dihydroxyphenylalanine, urea, formamide) that prevented, partially or totally, the activation of pro-tyrosinase. 4. The activation of pro-tyrosinase seems to be the result of a cleavage of the polypeptide chain that determines changes in tertiary or quaternary structure.

Kinetic Study of the Activation Process of a Latent Mushroom (Agaricus bisporus) Tyrosinase by Serine Proteases

“…Many enzymes occur as inactive precursors, named proenzymes or zymogens, to avoid undesirable intracellular reactions. Zymogen activation is involved in many physiological processes such as complement activation (Havsteen and Varo ´n, 1990), proinsulin-insulin conversion (Mihalyi, 1972), blood clotting (Wohl et al, 1980), digestion of proteins in the intestine (Cohen, 1976), and pro-tyrosinase activation (Pen ˜afiel et al, 1982;Galindo et al, 1983), among others. The kinetic analysis of several zymogen activation models has been previously reported in several theoretical studies (Varo ´n et al, 1987(Varo ´n et al, , 1988(Varo ´n et al, , 1990(Varo ´n et al, , 1993Va ´zquez et al, 1993).…”

Purification and primary structural characterization of prophenoloxidases from Aedes aegypti larvae

“…In most cases, the PO positive band(s) of crude or partially purified mosquito proPO samples showed a much higher molecular weight on SDS-PAGE than that of the deduced molecular mass of the proPO sequence. It has been accepted that proPO, once activated, is highly reactive, leading to the formation of a complex among themselves (such as homo-/hetero-dimer or trimer) (Penafiel et al, 1982;Hall et al, 1995;Kwon et al, ARTICLE IN PRESS Fig. 6.…”

Molecular and biochemical characterization ofParagonimus westermanityrosinase

“…TYR proteins in vertebrates are synthesized as zymogenic forms and converted into active molecules by a selective proteolytic cleavage (Peñafiel et al 1982). Phosphorylation of serine residues by a protein kinase is involved in the activation event (Park et al 1993).…”