RESUMO
The kinetics of glycerol uptake by the perfused rat liver were determined according to a model which includes membrane transport, intracellular phosphorylation and competitive inhibition of glycerol phosphorylation by L-glycerol 3-phosphate. The membrane transport obeys first-order kinetics at concentrations below 10 mM in the affluent medium. The K-m of the glycerol phosphorylation was 10 muM and the K-i of the L-glycerol 3-phosphate inhibition was 50 muM. The maximum activity (V) was 3.70 mumoles/min per g liver wet wt. These results are similar to in vitro kinetics of the glycerol kinase, except that K-i was found to be somewhat lower in the intact organ. At low glycerol concentrations, a steep concentration gradient exists across the liver cell membrane. The increase in the lactate to pyruvate concentration ratio during glycerol metabolism is related to the actual concentration of L-glycerol 3-phosphate, not to the rate of glycerol uptake.
Assuntos
Glicerol Quinase/metabolismo , Glicerol/metabolismo , Fígado/metabolismo , NAD/metabolismo , Fosfotransferases/metabolismo , Animais , Transporte Biológico , Biópsia , Membrana Celular/metabolismo , Feminino , Glicerofosfatos/farmacologia , Cinética , Lactatos/metabolismo , Modelos Biológicos , Perfusão , Piruvatos/metabolismo , RatosAssuntos
Frutose/metabolismo , Frutosefosfatos/biossíntese , Fígado/metabolismo , Trifosfato de Adenosina/metabolismo , Animais , Transporte Biológico , Radioisótopos de Carbono , Membrana Celular/metabolismo , Radioisótopos de Cromo , Inulina/metabolismo , Cinética , Fígado/citologia , Matemática , Perfusão , FosfotransferasesAssuntos
Metabolismo Energético , Gluconeogênese , Glicerol/metabolismo , Hipertireoidismo/metabolismo , Hipotireoidismo/metabolismo , Fígado/metabolismo , Glândula Tireoide/fisiologia , Acetoacetatos/metabolismo , Animais , Peso Corporal , Metabolismo Energético/efeitos dos fármacos , Feminino , Gluconeogênese/efeitos dos fármacos , Glicerol/farmacologia , Hidroxibutiratos/metabolismo , Hipertireoidismo/induzido quimicamente , Hipotireoidismo/induzido quimicamente , Iodo , Lactatos/metabolismo , Fígado/efeitos dos fármacos , Tamanho do Órgão , Perfusão , Piruvatos/metabolismo , Ratos , Tri-IodotironinaRESUMO
1. In the preceding paper [Kondrup (1979) Biochem. J.184, 63-71] the separation of two major fractions of hepatic triacylglycerol was described. One fraction contained triacylglycerol from the endoplasmic reticulum and from the Golgi apparatus. The other fraction contained triacylglycerol from the cytoplasmic lipid droplets. In the present paper possible precursor-product relationships between the two fractions were investigated by means of computer models. 2. The fatty acids present in di- and tri-acylglycerol in the fractions isolated in the time studies were analysed by gas chromatography. From this analysis the relative specific radioactivities, and contents, of palmitate in acylglycerols in the two fractions at the various time points were calculated. 3. A computer was used to predict relative specific radioactivities of pools in defined models of hepatic triacylglycerol metabolism. The acceptability of the models was evaluated by comparing predicted with measured relative specific radioactivities. 4. It is suggested that triacylglycerol in cytoplasmic lipid droplets does not originate (a) directly from triacylglycerol in the endoplasmic reticulum, (b) from a sub-pool of it or (c) directly from non-esterified fatty acids entering the cell. Rather, it is formed from diacylglycerol (and acyl-CoA) in the endoplasmic reticulum. Diacylglycerol, on the other hand, is furnished in part by hydrolysis of triacylglycerol in the endoplasmic reticulum. 5. This suggestion is discussed in relation to previous models of hepatic fatty acid metabolism.