Platelet-activating factor stimulates receptor-mediated formation of reactive oxygen intermediates in human monocytes.

Stimulation of production of reactive oxygen intermediates (ROI) was examined in human peripheral blood monocytes by luminol-dependent chemiluminescence. The dose-response curve characterizing the dependence of ROI production on the concentration of platelet-activating factor (PAF) showed that stimulation occurred within a concentration range of 2 x 10(-9)M to 5 x 10(-6)M. Transformation of the dose-response curve to an Eadie-Hofstee plot indicated that the process is characterized by two Km values.

[Inhibition of UV-induced accumulation of lipid peroxides by melanins and ommochromes].

The effect of screening pigments--melanin and ommochromes--on the UV-induced accumulation of lipid hydroperoxides by cardiolipin was studied. It was shown that the time dependence of lipid hydroperoxide accumulation at different UV irradiation intensities is linear. Addition of melanin or ommochromes results in a significant decrease of the lipid hydroperoxide accumulation rate.

The effect of thiamine pyrophosphate modification on its coenzyme function in a transketolase-catalyzed reaction.

The coenzyme function of TPP analogues: 4'-NH-methyl-TPP,6'-methyl-TPP and 6'-methyl-4-nor-TPP has been studied in a transketolase-catalyzed reaction. Their dissociation constants have been found with the aid of the circular dichroism method, and coenzyme activity has been determined in a complete transketolase reaction, involving the substrate-donor and the substrate-acceptor, and also at the intermediate stage (by the alpha-carbanionic intermediate oxidation rate). The coenzyme activity values have been found different and largely dependend on the nature of the substrates used.