INCREASED EFFECTIVE ACTIVITY OF RAT-LIVER CATALASE BY DIETARY RESTRICTION

While dietary restriction (DR) increases maximum life span in many ani mal species, the mechanisms by which this is achieved remain unclear. One possibility is that DR may act in part to reduce free radical leve ls by retarding age-related declines in rat liver catalase activity, W e measured liver cytosolic catalase activity at various times of day i n 9-12 month old male (BN X F344)F-1 rats fed ad libitum (AL) or subje cted to a 30% DR from 14 weeks of age. Catalase activity (expressed as mu mol-min(-1)-g liver(-1)) in both diet groups reached minimums at 0 600 h but activity was 26% higher in DR as compared to AL rats, This t raditional expression of catalase activity did not significantly diffe r between diet groups at other times of day. One must be careful in th e interpretation of such data, however, since catalase is rapidly inac tivated by its substrate (H2O2), thus displaying abnormal enzyme kinet ics. In order to avoid this difficulty we evaluated the time period du ring which the reaction remained linear and multiplied it by its activ ity to yield the effective catalase activity. Using this method we fou nd a significant increase in catalase activity in DR animals at severa l H2O2 concentrations during the light span. At 1800 h (the beginning of the dark span when the controls initiated peak food intake), fewer and smaller dietary differences were observed and no dietary effects w ere observed at 2400 h, These data suggest that DR reduces the rate of accumulation of inactive catalase and may contribute to an increased capacity in DR animals to remove free radicals.