Effect of bilirubin on activity and thermokinetic characteristics of brainplasma (synaptosomal) membrane NO synthase

NO synthase activity was discovered in the plasma (synaptosomal) membrane p articles isolated from the homogenate of adult rat brain (without cerebellu m) under conditions preventing protease attack and formation of reactive ox ygen species, The discovered NO synthase exhibited some properties of a neu ronal constitutive integral membrane enzyme add was inhibited by N-nitro-L- arginine. NO synthase activity decreased when bilirubin entered synaptosoma l membrane in vitro. Bilirubin caused the shift of the transition temperatu re in the temperature dependence of NO synthase activity in Arrhenius plots . The incorporation of bilirubin into synaptosomal membranes resulted an in crease in the apparent activation energy for NO synthase within a temperatu re range of 10-30 degrees C, The membrane NO synthase was susceptible to th e photodynamic effect of membrane-bound bilirubin molecules, Monomeric huma n serum albumin without organophilic ligands exerted protective effect towa rd NO synthase in bilirubin-containing membrane particles.