Free-radical generation by copper ions and hydrogen peroxide. Stimulation by Hepes buffer.

Hydroxyl radicals (OH.), generated by a phosphate-buffered Cu2+/H2O2 system, were detected by lucigenin-amplified chemiluminescence, deoxyribose degradation and benzoate hydroxylation. In each system the buffer, Hepes, was found to stimulate radical generation significantly. There are two main reasons for this effect: Hepes increases Cu2+ solubility in phosphate-buffered systems, and forms a complex with Cu2+ that is effective in generating OH. from H2O2. Pipes, a structurally similar buffer, and histidine, a known Cu2+ chelator, were found to have a similar effect. These data suggest that the crucial factor in such free-radical-generating systems is the availability of Cu2+, and that these actions of Hepes should be considered in the design of studies utilizing such systems.     

Inhibition of tyrosinase by indole compounds and reaction products. Protection by albumin.

Tyrosinase activity decreases as the reaction proceeds and is inhibited by L-3,4-dihydroxyphenylalanine oxidation products. Indole and tryptophan inhibit tyrosinase reaction and bovine albumin protects against end-product(s) inhibition or inactivation. Since the same tyrosinase reaction products are indole compounds and some authors reported the binding of indole derivatives with albumin, it is here suggested that indole intermediates of melanin synthesis inhibit or inactivate tyrosinase.     

Plasminogen activator production by human monocytes. I. Enhancement by activated lymphocytes and lymphocyte products.

Human monocytes, but not nylon wool column-nonadherent lymphocytes, produce plasminogen activator. The activity is found only in association with intact cells. Exposure of monocytes to activated lymphocytes or to lymphokine-rich supernatants enhances monocyte plasminogen activator production. The assay allows assessment of baseline and activated human monocyte function.