Studies on the latency of some glycosidases in rat liver lysosomes

Abstract

This thesis records results obtained between October, 1972 and September, 1975 in the Biochemistry Research Unit, University of Keele.
The latency of three glycosidases in intact rat liver lysosomes was examined with p-nitrophenyl substrates. The latency of the three enzymes observed with these substrates was unusually low, suggesting that p-nitrophenyl substrates can penetrate the membrane of intact lysosomes. A model, based on the heterogeneity of lysosomes with respect to their permeability properties, was proposed to explain these results. The validity of this model was examined by measuring the latency of oi-glucosidase with substrates of differing size (Chapter 3).
The latency of two exogenous lysosomal glycosidases with j>nitro- phenyl substrates was found to be much higher than that observed for the endogenous enzymes. The differing subcellular distribution of exogenous and endogenous enzymes suggests that the latency difference is connected with the vacuolar location of the exogenous enzymes: exogenous enzymes are located in vacuoles whose membrane is impermeable to p-nitrophenyl substrates (Chapter 4).
Lysosomes possess the enzymes which are capable of degrading nucleic acids to the level of nucleosides. In spite of their relatively high molecular weights, nucleosides were shown to be able to penetrate the membrane of intact lysosomes by demonstrating their inefficiency at providing prolonged osmotic protection to lysosomes. The relevance of these findings to the in vivo situation is discussed (Chapter 5).
Cysteine and ascorbate have both been previously reported to affect the stability of the lysosomal membrane. Neither substance had any measurable effect on the stability of rat liver lysosomes, as shown by the latency and sedimentibility of ?-glucosidase.(Chapters 6 and 7).
The validity of the use of leucyl ?-naphthylamidase as a lysosomal marker enzyme is discussed (Chapter 7).