Inhibition of norepinephrine autoxidation by a rat brain cortical factor.

Autoxidation in a physiological salt solution of 100-200 microM norepinephrine was measured, detecting formation of noradrenochrome spectrophotometrically at 480 nm. Samples from the 100,000 g supernatant of a rat cortex (10% w/v homogenate), diluted 100-fold by the reaction mixture, suppressed aminochrome formation approximately 90% for 5 h. The active principle, even in such high degree of dilution, proved to be a considerably more potent antioxidant than the metal chelating agent EDTA at optimal concentration. The antioxidant effect was most marked in the moderately alkaline pH range. The activity is associated with a relatively heat and acid stable, non-dialyzable protein (mol wt greater than 50,000), found in the 100,000 g supernatant.