Gylcine-14C incorporation into the plasma membrane proteins of normal and regenerating liver

Incorporation of 14C-glycine in plasmatic membrane proteins of the intact and regenerating liver was studied at the beginning of G1 period of the cell cycle. The electrophoretic study of 0.05 M Na2CO3 soluble plasmatic membrane proteins of the regenerating liver showed that maximal incorporation of 14C-glycine was associated with the proteins having molecular weight of about 60 000. The pattern of incorporation of 14C-glycine in different fractions of 0.05 M Na2CO3 insoluble proteins of the plasmatic membranes of the intact and regenrating liver did not differ essentially.     

Metabolism of L-(U-14C)valine, L-(U-14C)leucine, L-(U-14C)histidine and L-(U-14C) phenylalanine by the isolated perfused lactating guinea-pig mammary gland.

1. The incorporation of L-[U-14C]leucine, L[U-14C]histidine and L-[U-14C]phenylalanine into casein secreted during perfusion of isolated guinea-pig mammary glands was demonstrated. 2. The extent of incorporation of label into casein residues was consistent with their being derived from free amino acids of the perfusate plasma. 3. The mean transit time of the amino acids from perfusate into secreted casein was approx. 100 min. 4. Whereas radioactive histidine and phenylalanine were incorporated solely into milk protein, radioactivity from [U-14C]valine was also transferred to CO2 and to an unidentified plasma component, and from [U-14C]leucine to plasma glutamic acid. 5. Evidence from experiments with [U-14C]phenylalanine suggests that, as in rats, but in contrast with ruminant species, guinea-pig mammary tissue does not possess phenyl alanine hydroxylase activity. 6. The results are discussed in relation to the possible role of essential amino acid catabolism in the control of milk-protein synthesis.     

The incorporation of isotopic carbon (14C) into the cerebral glycogen of rabbits

1. The incorporation of (14)C into the brain glycogen of conscious rabbits with labelled glucose, bicarbonate and glutamate as precursors has been studied. 2. Substantial incorporation from all these precursors was demonstrated after an interval of 5hr. from their injection. 3. With [(14)C]glucose maximal incorporation occurred at about 8hr. from the time of injection. 4. Hydrocortisone led to increased incorporation of (14)C from labelled glucose. 5. Some comparisons between the turnover of brain glycogen and that of skeletal and cardiac muscle are reported.     

Dynamics of [2-14C]pyruvate incorporation into liver phospholipid fractions in rats consuming water or ethanol

The animals with preference to ethanol as compared to those with preference to water show an increase in the specific radioactivity of glycerol moiety of liver phosphatidylethanolamine 1 hour and in that of glycerol component of phosphatidylcholine 3 hours after the [2-14C]-pyruvate administration.     

Incorporation of fucose into HeLa cell plasma membranes during the cell cycle

The metabolism of HeLa cell plasma membranes during the cell cycle was studied by following the incorporation of radioactive precursor l-[³H]fucose into plasma membranes of synchronized cells. Maximal incorporation of the radioactive precursor was observed in late S phase of the cell cycle. This discrete period of increased incorporation of precursor into the plasma membranes implies the existence of a distinct control mechanism which may relate cell surface phenomena to the cell cycle.     

Decreased incorporation of L-[U-14C]serine into phosphatidylserine by polymorphonuclear leukocytes during phagocytosis

A decreased rate of L-[U-14C]serine incoroporation into phosphatidylserine of polymorphonuclear leukocytes exposed to starch granules was observed. L-[U-14C]serine uptake was also depressed under identical conditions. The degree of reduction in specific radioactivity of phosphatidylserine was parallel to that of L-[U-14C]serine uptake. Both uptake and efflux of 45Ca2+ were enhanced in cells with starch granules, but no significant change in cellular calcium levels was detected. These results suggest that the reduced L-[U-14C]serine incorporation into phospholipids may be attributable to decreased availability of this amino acid. The involvement of Ca2+ fluxes in phosphatidylserine synthesis in intact leukocytes cannot, however, be excluded.