Alterations in surface carbohydrates and in some functional properties of liver lysosomal membrane in vitamin A-deficient rat

Abstract

A significant decrease in total carbohydrates and particularly in mannose, galactose and sialic acid has been observed in vitamin A-deficient rat liver lysosomal membrane. These alterations adversely affect the membrane permeability and structure-linked latency of the lysosomal enzymes. Significant reduction in the pH-dependent in vitro binding of the lysosomal arylsulfatase B to the highly purified membrane has been observed in vitamin A deficiency. This is attributed to the decrease in electro-negativity, mainly due to the observed reduction in negatively-charged sialic acid residues on the outer side of the membrane. Similar reduction in sialic acid content on the inner side of the membrane affects the microenvironment in the lysosomes. Intralysosomal pH, measured by computing the proteolytic activity of lysed lysosomes and of phagolysosomes, endocytosed with denatured 131I-labelled human serum albumin, is slightly but consistently higher in vitamin A-deficient groups compared to that in control one. This is reflected in the low rate of degradation of the entrapped proteins in vitamin A deficiency. The possible physiological significance of the observations is discussed with special reference to the loss of surface carbohydrates, particularly sialic acid, in vitamin A-deficient rats.