Compartmentation of lysosomes in neurones and neuropil and a new neuronal marker

Abstract

The activity of 9 acid hypdrolases and 2 alkaline hydrolases has been determined in cortical subcellular fractions, separated neuronal and neuropil cell fractions, and neuronal and neuropil subcellular fractions, from the rat. A modification of Rose Method I for the bulk separation of neuronal and neuropil fractions, designed to reduce possible contamination by liberated lysosomes, was introduced. In general, the acid hydrolases were concentrated in the crude ‘mitochondrial’ and ‘lysosomal’ subcellular fractions, though some showed a bimodal distribution. The alkaline hydrolases were more generally distributed. All enzymes were more concentrated in the neuronal than the neuropil cell fractions. The acid hydrolases could be divided into 3 groups. Group I contained β-glucosidase, acid phosphatase, β-glucuronidase and arabinosidase, group II aryl-sulphatase, cathepsin, acid DNAse and β-glucosaminidase, and group III β-galactosidase. The neuronal-neuropil activity ratio for group I was between 1.4 and 3.4, for group II between 5.8 and 6.8 and for group III, 9.9 Solubilisation of the enzymes with Triton X-100 slightly enhanced the activity, but did not affect the neuronal-neuropil activity ratios of the enzymes β-glucuronidase, β-glucosidase and β-galactosidase. After subcellular fractionation of the neuronal and neuropil fractions the neuronal-neuropil compared with neuropil lysosomal protein; (b) the cellular compartmentation of cerebral lysosomes. The significance of these observations in terms of the relationship between neuronal and neuropil metabolism is discussed and appropriate predictions made. The enzyme β-galactosidase is proposed as a new neuronal marker.