Kinetics of internalization and degradation of asialo-glycoproteins in isolated rat hepatocytes.
The rate constants for internalization of surface-bound asialo-orosomucoid by hepatocytes were 0.040 min-1 at 20 degrees C, 0.18 min-1 at 30 degrees C and 0.28 min-1 at 40 degrees C. At 40 degrees C, internalization accounted for most of the increase in cell-associated radioactivity. The activation energy over the temperature range 20 to 40 degrees C was 68 +/- 7 (S.D.) kJ/mol. At 10 degrees C, most of the cell-associated asialo-orosomucoid was bound to the cell surface in a reaction which followed ordinary chemical kinetics. Pre-incubation of hepatocytes with a large concentration of unlabelled asialo-orosomucoid did not influence the uptake of subsequently added 125I-asialofetuin; neither was degradation of 125I-asialo-fetuin affected in this experiment. The fractional rate of degradation (the fraction of cell-associated asialo-fetuin which was degraded per unit time) was constant over a twelve-fold range of intracellular asialo-fetuin concentrations. Increasing the temperature from 20 to 30 degrees C produced approximately a ten-fold increase in the rate of degradation of either asialo-fetuin or asialo-orosomucoid. The average activation energies of degradation over the range 20 to 40 degrees C were 125 kJ/mol for asialo-fetuin and 149 kJ/mol for asialo-orosomucoid; however, the Arrhenius plots were not straight lines over this temperature range.
D000818:Animals; D001212:Asialoglycoproteins; D002462:Cell Membrane / Q000378:metabolism; D004705:Endocytosis; D060748:Fetuins; D007700:Kinetics; D008099:Liver / Q000166:cytology* / Q000378:metabolism; D009961:Orosomucoid / Q000031:analogs & derivatives* / Q000378:metabolism; D051381:Rats; D013696:Temperature; D000509:alpha-Fetoproteins / Q000378:metabolism*
D001212:Asialoglycoproteins; D060748:Fetuins; D009961:Orosomucoid; D000509:alpha-Fetoproteins; C017029:asialofetuin; C017030:asialoorosomucoid