RAT-KIDNEY LYSOSOMES: ISOLATION AND PROPERTIES

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Abstract
The activities of lysosomal enzymes in the cortexes and medullas and the principal subcellular fractions of rat kidney were measured. A method is described for the isolation of rat-kidney lysosomes and a detailed analysis of the enzymic composition of the lysosomes is reported. Enzyme analysis of the other principal subcellular fractions is included for comparison. Studies of the distribution of a-glucosidase showed that the lysosomal fraction contained only 10% of the total enzyme activity. The microsomal fraction contained most of the particulate a-glucosidase. Lysozyme was concentrated mainly in the lysosomal fraction with only small amounts present in the microsomal fraction. Lysosomal a-glucosidase had optimum pH 5 whereas the microsomal form had optimum pH 6. Both lysosomal and microsomal lysozyme had optimum pH 6.2. The stability of lysosomal suspensions was studied. Incubation at 37[degree] and pH 7 resulted in first an increased availability of enzymes without parallel release of enzyme. This was followed by a 2nd stage during which the availability of enzymes was closely related to the release of enzymes. These changes were closely paralleled by changes in light-scattering properties of lysosomes. The latent nature of the a-glucosidase and lysozyme of intact kidney lysosomes was demonstrated by their graded and parallel release with other typical lysosomal enzymes. Isolated lysosomes were unstable at pH values lower than 5, most stable at pH 6-7 and less stable at pH 8-9. Lysosomes were not disrupted when the osmolarity of the suspending medium was decreased from 0.6 M to 0.25 M. The discussion compares the properties and composition of kidney lysosomes, liver lysosomes and the granules of macrophages. The possible origin of the lysozyme in kidney lysosomes by reabsorption of the lysozyme in blood is discussed.