Lysosomal protein degradation in experimental hyperphenylalaninaemia

The influence of alpha-methylphenylalanine-induced hyperphenylalaninaemia (HYP) on the lysosomal protein degradation system in brain and liver of suckling rats was investigated. In both tissues cathepsin D and L activities, measured at 5, 10 and 15 days post partum (p.p.), exhibited no differences between experimental and control animals. N-Acetyl-beta-D-glucosaminidase (NAGase) activity in brain, measured at 10 and 15 days p.p., was not affected by HYP either. The release of valine and lysine from liver and brain homogenates respectively, serving as a measure for the lysosomal content of degradable proteins, was not influenced by HYP. Lysosomal integrity during incubation of homogenate was monitored by the recovery of NAGase activity in the cytosolic supernatant, and by the relative NAGase activity in total homogenates in the absence of the lysosome disrupting detergent Triton X-100. In conclusion, experimental HYP appears unlikely to influence the lysosomal protein degradation system in brain and liver of suckling rats.