Effect of feeding protein deficient diet on phospholipid turnover and protein kinase C mediated protein phosphorylation in rat brain.

Feeding of protein deficient diet is known to alter the transmembrane signalling in brain of rat by reducing total protein kinase C (PKC) activity. Phospholipid metabolism regulates the activation of PKC through generation of second messengers and the extent of PKC activation accordingly influences the magnitude of phosphorylation of its endogenous substrate proteins. Thus it was speculated that ingestion of protein deficient diet may modify the turnover rate of membrane phospholipids and magnitude of phosphorylation of endogenous substrate proteins of PKC. The experiments were conducted on rats fed on three different types of laboratory prepared diets viz. casein (20% casein), deficient (4% protein, rice flour as source of protein) and supplemented (deficient diet supplemented with L-lysine and DL-threonine) for 28 days. The metabolism of phosphoinositides (PIs) and phosphatidyl choline (PC) was studied by equilibrium labeling with [3H] myo inositol and [14C methyl] choline chloride respectively. The phosphorylation of endogenous substrate proteins of PKC was studied by using 32P-gamma-ATP followed by SDS-PAGE and autoradiography. The results suggest that in deficient group, there is an increased incorporation of [3H] myo inositol in PIs and inositol phosphate pool in comparison to the casein group. The phosphatidyl inositol (PI) turnover reduced, although there was a marginal increase in the phosphatidyl inositol monophosphate (PIP) and phosphatidyl inositol bis phosphate (PIP2). Supplementation of diet showed a reversal of the pattern towards control to a considerable extent. In the deficient group, PC metabolism showed an increased incorporation of [14C methyl] choline in choline phospholipids but decreased incorporation in phosphoryl choline in comparison with the casein group. The increase in total PC contents was significant but marginal in residue contents. The turnover rate of PC increased only marginally and that of residue declined. Supplementation of diet reduced the total contents of PC and residue, but the turnover rate of PC and residue remained still higher. Phosphorylation of endogenous proteins showed four different proteins of 78, 46, 33 and 16 kDa to be the substrates of PKC in casein group. In deficient group, phosphorylation of these proteins increased markedly while supplementation of diet had a reversing effect rendering the values to be intermediate between casein and the supplemented group. The changes in phospholipid metabolism and in phosphorylation of endogenous substrate proteins of PKC suggest that dietary protein deficiency causes alterations in transmembrane signalling mechanism in rat brain. These effects are partially reversed by improving the quality of proteins in the diet.

Dietary protein deficiency induced changes in protein kinase C activity and phospholipid metabolism in rat hepatocytes.

Dietary protein deficiency is known to alter the protein kinase C activity in various tissues of rats. Protein kinase C activity is influenced by the metabolism of membrane phosphoinositides and phosphatidyl choline (PC). For metabolic studies, hepatocytes have been the cells of choice of various workers. Therefore, studies on protein kinase C and these phospholipids were conducted in hepatocytes of rats maintained on three different diets viz. casein (20% protein) deficient (4% protein, rice flour as source of protein) and supplemented (deficient diet supplemented with L-lysine and DL-threonine) diet for 28 days. The protein deficiency in diet led to a decline in protein kinase C activity (P < 0.01) without effecting its translocation, an increase in phosphatidyl inositol 4,5-bisphosphate (P < 0.001) and a decrease in phosphatidyl inositol 4-monophosphate and phosphatidyl inositol (P < 0.01) but did not alter the PC contents, as compared to the casein group. Supplementation of deficient diet with L-lysine and DL-threonine could considerably reverse the effect of deficiency of protein in diet. The results suggest that quality of dietary protein is mainly relevant for maintaining phospholipid metabolism and physiology of hepatocytes and thus the signalling mechanism in these cells.

Differential activity of protein kinase C in alveolar and peritoneal macrophages.

The characteristics of protein kinase C activity present in guinea pig alveolar and peritoneal macrophages have been compared and examined. The activity is predominantly cytosolic with preference for phosphatidyl serine as cofactor over other phospholipids. K(m) of protein kinase C for ATP is 30.30 and 54.05 microM in alveolar and peritoneal macrophages respectively. Scatchard plot analysis shows heterogenous binding sites for [3H]PDBu in alveolar macrophages in contrast to peritoneal macrophages showing homogeneous type of binding sites. PMA activates protein kinase C in a dose-dependent manner and shows downregulation at higher concentration in both alveolar and peritoneal macrophages. Endogenous proteins of molecular masses 77, 47, 37 and 16.5 kDa in alveolar macrophages and 77, 47, 38 and 15.5 kDa in pertioneal macrophages are phosphorylated by PKC. These findings suggest that alveolar and peritoneal macrophages possess two different types of protein kinase C activities but phosphorylate similar proteins and exhibit functional similarities in these cells.

Effect of dietary protein manipulation on translocation of protein kinase C activity in various tissues of rats.

Ingestion of protein deficient diet is known to decrease the enzyme load, particularly drug metabolising enzymes in liver. It also leads to decrease in polyphosphoinositide pool in brain and kidney. Therefore, changes in protein kinase C activity and its translocation were speculated and studied in brain, lung, heart, spleen, liver and kidney of rats maintained on three different diets, viz. casein (20% protein) deficient (4% protein, rice flour as protein source) and supplemented (deficient diet supplemented with L-lysine and DL-threonine), for 28 days. A significant alteration in total protein kinase C activity and/or its translocation was observed in these tissues in the deficient group in comparison to casein group. Supplementation of diet with L-lysine and DL-threonine could partially reverse the affect. These changes in protein kinase C activity and its translocation indicate alteration in the mechanism of signalling system in dietary protein deficiency and hence an altered response of tissues to the external stimuli in dietary protein deficiency.

Phosphoinositides of sheep platelets plasma membranes.

Phospholipid composition of sheep blood platelets and its various plasma membrane fractions have been analyzed. Based on their flotation rates in discontinuous sucrose density gradient centrifugation, three membrane fractions were isolated. 5'-Nucelotidase and alkaline phosphatase were distributed nearly equally in all the three membrane fractions. However these membrane fractions showed differences in the distribution of phosphatidyl ethanolamine, phosphatidyl choline and phosphoinositides. Phosphatidyl ethanolamine was predominant in fraction I (11.05 micrograms PLP/mg protein) while phosphatidyl choline was predominant in fractions II and III (110.10 and 68.30 micrograms PLP/mg protein respectively). Phosphatidyl inositol (Ptd-InsP) was equally distributed in all three membrane fractions. However, both Ptd-InsP and phosphatidyl inositol 4,5-bisphosphate were about 4-fold higher in fraction II (73.55 and 89.89 micrograms PLP/mg protein respectively).

Hepatic mitochondrial membrane lipid environment and protein nutrition.

Effect of feeding rice diet with and without lysine and threonine supplementation on hepatic mitochondria and its inner and outer membrane proteins, enzymes and phospholipids has been studied. The exchange of phosphatidylcholine and phosphatidylethanolamine between microsomes and mitochondria has also been studied under these conditions. Deficient diet lead to significant decrease in proteins as well as activities of monoamine oxidase, succinate dehydrogenase, cytochrome a + a3 and cytochrome c in mitochondria and its inner and outer membranes. Feeding of the deficient diet also significantly reduced total phospholipids and PC in mitochondria and its outer mitochondrial membrane. In the inner mitochondrial membrane, only PE and cardiolipin were reduced. The incorporation (DPM/microgram PLP) of [methyl-3H]choline and [methyl-14C]methionine into PC of mitochondria and its outer membrane and that of 32Pi into PC and PE of outer mitochondrial membrane but only into PC of inner mitochondrial membrane were significantly reduced in the deficient group. The exchange rates of PC and PE between microsomes and mitochondria were reduced in the deficient group. Supplementation of the deficient diet with lysine and threonine profoundly improved the above biochemical lesions as compared to casein fed rats.