The Conversion of Glucose Carbon Into Protein in the Brain and Other Organs of the Rat

Abstract

WHEN [14C]glucose is administered in oiuo, part is oxidized to CO,, part is stored as glycogen and part is used for the synthesis of amino acids and other compounds in the tissues (WINZLER et al., 1952;PROCHOROVA, 1954; ALLWEIS and MAGNES, 1958a,b; GEIGER, 1958;BUSCH et al., 1960). ROBERTS, FLEXNER and FLEXNER (1959) reported a relatively high rate of conversion of glucose carbon into protein in the liver and brain in the mouse. They found that the distribution of I4C in the different amino acids of the proteins was different in the two organs : there was a greater incorporation of I4C into alanine than into glutamic acid in the liver, whereas in brain tissue the converse was true.The object of the present work was to study the conversion of glucose-carbon into protein in the rat brain. Orientating experiments were first carried out to find out to what extent carbon from [14C]glucose is incorporated in the free amino acids and proteins of other organs besides the brain. The incorporation was studied for a period of up to 12 hr and the distribution of I4C was examined in the dicarboxylic, neutral and basic amino acid fractions. METHODSMale or female littermates (100-150 g) of a Wistar albino strain of rat were used. D-[UJ~C]-Glucose (410 pclmg) was obtained from the Radiochemical Centre, Amersham, England. The isotopic purity determined by the suppliers by dilution with glucose and conversion to the pentaacetate was 100 per cent 14C: analysis by paper chromatography gave 99 per cent purity both in n-butanolethanol-water and in phenol-water. Each animal received 0.2 ml of a solution of D-[u-' *C]glUCOSe (5 pc) containing 2 mg of added carrier glucose by subcutaneous injection. The animals were decapitated with a guillotine at intervals between 0 3 and 12 hr after injection of radioactive glucose. The brains and other organs were quickly removed, blotted on filter paper, frozen in liquid nitrogen and then kept at -20" until analysed. Blood was taken immediately after decapitation in a 25 ml beaker coated with Na-oxalate and 1 ml was pipetted with a similarly coated pipette into 5 ml of 10 per cent (w/v) trichloroacetic acid (TCA).Protein fractions. Brain, liver, kidney, spleen, heart, blood and skeletal muscle (gastrocnemius) were taken for analysis. The organs were weighed on a torsion balance, defrosted in 5 ml of ice-cold 10% TCA in a MSE-homogenizer tube (Measuring & Scientific Equipment Ltd., London), and then homogenized for 1 min at 0". The sediment obtained by centrifugation for 15 min at 1000 g was resuspended in 5 ml of TCA at 0" and the treatment was repeated with 4 consecutive 5 ml portions of TCA. The combined TCA-extracts were kept for analysis of acid-soluble amino acids.The residue after TCA extraction was treated with organic solvents to remove lipids as described by VRBA, FOLBERGROV~ and KANTBREK (1957). The tissue lipids were extracted consecutively with acetone, ethanol-ethyl ether (3 : I, v/v), chloroform-methanol (2 : 1 , v/v) and ether. The combined lipid extracts were evaporated to dryness ...

Assimilation of glucose carbon in subcellular rat brain particles in vivo and the problems of axoplasmic flow

“…This is in satisfactory agreement with the value of 0.24% deduced from data obtained from different experiments by different authors who made use of either rats or mice of various strains (Steele, 1954;Vrba et al 1962;Vrba, 1966).…”

Biochemistry of Selected Amino Acids

“…(112 -114) However, a recent report from part of the same group did not confirm the earlier findings for glucose conversion to essential amino acids. (115) Many investigators have found rapid conversion in vivo of glucose carbon to nonessential amino acids in brain of mouse, (116.117) of rat both normal (118)(119)(120)(121) and hepatectomized, (121) of cat, (122) and of sheep. (123) Perfusion of cat brain with solutions containing labeled glucose has also been studied.…”

Whole-body autoradiographic study of (U-14C) galactose in mice and its biochemical analysis.

“…Therefore, galactose metabolism in the brain might be limited. Vrba (36), Vrba et al (39) and Shimada et al (28) showed the rapid incorporation of 14C from 14C-glucose into free amino acids in rat and mouse brains. Our present findings may be consistent with the data of these reports and suggest that most of 14C may be taken up into the brain after being converted into glucose in certain organs (30) and then metabolized further into such free amino acids as glutamate, aspartate, GABA, alanine and glycine.…”