Hydrolase activities in brain of neurological mutants: cerebroside galactosidase, nitrophenyl galactoside hydrolase, nitrophenyl glucoside hydrolase and sulphatase.

(1) The brains of 17-day-old quaking and jimpy mice were compared with those of the corresponding normal phenotypes. The concentrations of cerebroside and sulphatide were found to be markedly lower in the affected mutants, while the relative amounts of ceramide and free fatty acid appeared normal. (2) The concentration of cerebroside glactosidase was not significantly abnormal in the jimpy mice but was about 17 per cent lower in quaking mice. In contrast, the relative amount of the enzyme that could be dispersed by sonication was considerably higher in the jimpy animals. It is suggested that this increase is a causative factor in the aetiology of the latter disease. (3) The concentrations of other acid hydrolases were determined, as well as the relative amounts dispersible by sonication. No difference was seen between the phenotypes with NPGalH, NPGluH, and nitrocatechol sulphate hydrolase. (4) An improved solvent system for the TLC detection of ceramide in brain lipids is described. A NUMBER of neurological mutants of the mouse central nervous system have been characterized genetically and histologically (SIDMAN, GREEN and APPEL, 1965). In the quaking and jimpy mutants, the content of myelin, cerebroside and cerebroside sulphate is greatly reduced (SIDMAN, DICKIE and APPEL, 1964; BAUMANN, JACQUE, POLLET and HARPIN, 1968). It seemed possible that the cerebroside-cleaving enzyme, cerebroside galactosidase (cerebrosidase), is over-active in the affected animals. The excessive activity could be the result of overproduction of the enzyme or of a high proportion of physiologically active enzyme. Cerebrosidase is largely particle-bound, apparently in lysosomes (BOWEN and RADIN, 1968). Lysosomal enzymes are known to become partially or completely dispersed when the suspended particles are stressed physically (SAWANT, SHIBKO, KUMTA and TAPPEL, 1964). Such dispersion may take place in the intact animal and the proportion of the enzyme that is dispersed may determine the functional activity of each lysosomal enzyme. It is thus possible that the level of total cerebrosidase could be normal or even subnormal in the mutants, but that the functional activity is high. An investigation of these possible explanations is reported here, together with a comparison with other acid hydrolases that are apparently lysosomal. This work supported in part by a Public Health Service Grant, No. NB-03192, from the National Institute for Neurological Diseases and Blindness. a Present address : Unilever Research Laboratory, Isleworth, Middlesex, England. Abbreviations used: NPGalH, p-nitrophenyl B-D-galactoside hydrolase; NPGluH, p-nitrophenyl P-D-glucoside hydrolase.