Synthesis and phosphorylation of macrophage membrane proteins in protein deficient rat.

Changes in the biosynthesis and phosphorylation of rat peritoneal macrophage membrane proteins induced by protein malnutrition have been studied. The results clearly indicate that the biosynthesis of high molecular weight proteins (45-200 kDa) and their phosphorylation are significantly reduced in the macrophages isolated from protein deficient (4% protein-fed) rats compared to the control group fed 20% protein diet. Lipopolysaccharide (LPS) treatment both in vivo and in vitro enhanced the synthesis and phosphorylation of these proteins in both control and protein deficient groups; however, the extent of enhancement was much less in the deficient group. These results indicate that besides the down regulation of these membrane proteins, protein malnutrition seems to make these macrophages less responsive to potent immuno stimulants like LPS.

Enumeration of macrophage carbohydrates in protein-deficient rats: relation to cell surface properties.

In order to study the effect of protein malnutrition on macrophage glycoproteins the carbohydrate composition of peritoneal macrophages from protein-deficient rats has been studied by paper chromatography and HPLC. The results show that the carbohydrate content of resident cells recovered from protein-deficient group was significantly greater than control and decreased on prolonged incubation. In the protein-deficient samples there was a significant decrease in the content of galactose, fucose and galactosamine known to be binding to specific ligands and increase in glucose and mannosamine. In both control and deficient groups, thioglycollate (TG) elicitation resulted in higher total sialic acid content. Prolonged incubation (18 hr) caused an elevation of sialic acid levels in the resident cells, whereas a drastic reduction was observed in the TG elicited cells. In the protein-fed (20%) group, the cell surface sialic acid which contributes to the negative charge of the cells, reduced significantly on culturing the TG cells but not the resident cells. In the protein-deficient group, this effect was seen in the resident cells also; in the TG cells the cell surface sialic acid was significantly low at the isolation stage suggesting that these cells had become comparatively more positively charged in vivo itself. This observed reduction could be correlated to the enhanced sialidase levels in these cells. These protein deficiency related changes in the carbohydrate composition of macrophages could lead to modification of their receptor activity and charge related functions.

Changes in rat liver mitochondrial lipids in vitamin A deficiency.

The alterations in the lipid profiles of rat liver mitochondria due to vita min A deficiency were studied. The amount of total lipids and phospholipids were decreased with a concomitant increase in triglycerides and cholesterol levels in mito chondria, isolated from vitamin Α deficient animals. Of particular significance was the observation that the content of lysolecithin, a potent cytolytic agent, was increased. An analysis of individual fatty acids showed that the percentage of polyunsaturated fatty acids was decreased significantly in vitamin A deficiency. Further, mitochondria from vitamin Α deficient animals, when incubated in 0.1 Μ Tris HCl buffer (pH 7.4) in vitro, produced increased amounts of malondialdehyde and lipofuchsin pigments indicating increased susceptibility of the mitochondrial membrane to peroxidative damage. These results suggest a possible role of vitamin A in the prevention of the decomposition of structural lipids.

Binding of arylsulphatase Β to isolated rat liver lysosomal membranes.

Binding of arylsulphatase Β to isolated rat liver lysosomal membrane has been studied at 37°C. The binding is strongly pH dependent and is governed by ionic strength of the medium. Experimental evidence is given for the ability of the enzyme to dissociate from the firmly formed membrane enzyme complex. The dissociation rate is greatly accelerated by raising the buffer molarity. Neuraminidase treatment of the membrane causes significant reduction in its binding ability to the enzyme. This suggests that sialic acid groups participate, presumably by maintaining surface negativity of the membrane, at a stage of enzyme membrane interaction process which precedes the internalization of the lysosomal enzymes in the lyso omes.