KINETICS OF INTERNALIZATION AND DEGRADATION OF ASIALO-GLYCOPROTEINS IN ISOLATED RAT HEPATOCYTES

  • 1 January 1980
    • journal article
    • research article
    • Vol. 23  (1) , 104-109
Abstract
The rate constants for internalization of surface-bound asialo-orosomucoid by hepatocytes were 0.040 min-1 at 20.degree. C, 0.18 min-1 at 30.degree. C and 0.28 min-1 at 40.degree. C. At 40.degree. C, internalization accounted for most of the increase in cell-associated radioactivity. The activation energy over the temperature range 20-40.degree. C was 68 .+-. 7 (SD) kJ/mol. At 10.degree. 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 unlabeled 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/unit time) was constant over a 12-fold range of intracellular asialo-fetuin concentrations. Increasing the temperature from 20-30.degree. C produced .apprx. a 10-fold increase in the rate of degradation of asialo-fetuin or asialo-orosomucoid. The average activation energies of degradation over the range 20-40.degree. C were 125 kJ/mol for asialo-fetuin and 140 kJ/mol for asialo-orosomucoid; the Arrhenius plots were not straight lines over this temperature range.