Nitric oxide regulates peroxisomal enzyme activities.

We have previously shown that peroxisomes are involved in the production and detoxification of reactive oxygen species and that peroxisomal functions are damaged by such oxygen species. Since nitric oxide is not only a cellular messenger, but also a free radical, it would be interesting to detect a connection between nitric oxide levels and peroxisomal enzyme activities. To determine if nitric oxide has an effect on the activities of peroxisomal functions and whether this effect is based solely on its chemical properties as reactive oxygen species or its action as a second messenger, effectors of the cellular nitric oxide level were applied to a cell model (human skin fibroblasts in culture) or directly to the enzymatic assays or both. If applied to the monolayer at non-cytotoxic concentrations, N-nitro-L-arginine methyl ester hydrochloride, an inhibitor of nitric oxide synthase (EC 1.14.13.39), increased catalase (EC 1.11.1.6) activity by more than 10% and decreased the activity of the peroxisomal fatty acid oxidation system by more than 10%. The effect was concentration-dependent. L-Arginine had the contrary effect. Combinations of L-arginine and N-nitro-L-arginine methyl ester hydrochloride compensated one another. If applied directly to the assays, S-nitroso-N-acetylpenicillamine and sodium nitroprusside inhibited catalase activity in a concentration-dependent manner. Sodium nitro-prusside had no effect on the peroxisomal beta-oxidation system unless cells were pretreated with N-nitro-L-arginine methyl ester overnight (50% inhibition). The results show a differential effect for the application of nitric oxide-effectors on fibroblast monolayers, cell suspensions and under assay conditions. Depending on the conditions of the incubation, nitric oxide applied to the cell monolayer at low doses acts as a second messenger in cells rather than as reactive oxygen species. Under assay conditions the effect of nitric oxide is more likely that of a reactive oxygen species because it inhibits all measured enzyme activities.