Protecting or promoting effects of spermine on DNA strand breakage induced by iron or copper ions as a function of metal concentration.

Polyamines are ubiquitous polycations that participate in cellular processes such as growth, differentiation and cell death. Among the different functions ascribed to these organic cations, the polyamine spermine is known to protect DNA from the damage produced by reactive oxygen species (ROS) generated by different agents including copper ions. We have found that spermine exerts opposite effects on DNA strand breakage induced by Fenton reaction depending on metal concentration.

Kinetic study of the interaction between frog epidermis tyrosinase and chloride.

The effect of halide ions on frog epidermis tyrosinase has been characterized with the trypsin-activated enzyme. At pH 7, the order of inhibition is I- greater than Br- greater than Cl- greater than F-. Chloride, the most extensively studied halide, shows a competitive pattern with respect to the substrate, L-DOPA.

Steady-state study of the mechanism of dopa-oxidase activity of tyrosinase.

The mechanism of the dopa-oxidase activity of frog epidermis tyrosinase has been studied. Initial reaction rates have been measured as function of substrate concentrations, L-dopa and oxygen, in the presence and absence of an inhibitor, product of the reaction. Initial reaction rates versus substrate concentrations, without inhibitor, show a linear dependence in the double-reciprocal space, that discarded Ordered and Random mechanisms.

Kinetic study of the activation process of frog epidermis pro-tyrosinase by trypsin.

1. The rate of tyrosinase formation has been calculated by coupling the activatory process of frog epidermis pro-tyrosinase by trypsin to the oxidation of L-DOPA to dopachrome. Under certain conditions ([trypsin]/[pro-tyrosinase] greater than or equal to 300), the lag period of the coupled reactions, tau, is independent of trypsin concentration.

The process for the activation of frog epidermis pro-tyrosinase.

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.