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Binding of epidermal growth factor (EGF) and insulin to human liver microsomes and Golgi fractions
Abstract:
Microsomes and Golgi fractions were isolated from 13 human liver samples without local malignancy. Binding of insulin to microsomes (per cent per 0.5 mg protein) was 14.4 +/- 7.9% with two classes of receptors: K1 = 1.4 nM, R1 = 0.28 pmol/mg; K2 = 8.1 nM, R2 = 0.62 pmol/mg. The binding was insignificantly lower than in rats. Binding of EGF was only 3.4 +/- 1.7% with two classes of receptors: K1 = 1.4 nM, R1 = 0.06 pmol/mg; K2 = 10.8 nM, R2 = 0.22 pmol/mg; the binding was much lower than in rats (26.3 +/- 5.8%). Binding of insulin to Golgi fraction (per cent per 0.1 mg protein) was 5.5 +/- 0.4% with straight line Scatchard plot; Kd = 5.6 nM, Ro = 3.06 pmol/mg; it was only half of that found in rats. In one case of hepatoma, the binding of insulin to microsomes was normal but that of EGF very low.
Insights
Human liver microsomes and Golgi fractions show distinct insulin and epidermal growth factor (EGF) receptor binding. Insulin binding is comparable to rats, while EGF binding is significantly lower, suggesting species-specific receptor differences.
Area of Science:
- Biochemistry
- Cell Biology
- Hepatology
Background:
- Insulin and epidermal growth factor (EGF) are crucial signaling molecules.
- Liver microsomes and Golgi apparatus are key cellular components involved in protein processing and signaling.
Purpose of the Study:
- To investigate the binding characteristics of insulin and EGF receptors in human liver microsomes and Golgi fractions.
- To compare these binding parameters with those observed in rat liver.
Main Methods:
- Isolation of microsomes and Golgi fractions from human liver samples.
- Radioligand binding assays to quantify insulin and EGF receptor binding.
- Scatchard analysis to determine receptor affinity (Kd) and density (Ro).
Main Results:
- Human liver microsomes exhibited two classes of insulin receptors (K1=1.4 nM, R1=0.28 pmol/mg; K2=8.1 nM, R2=0.62 pmol/mg), with binding comparable to rats.
- EGF binding to microsomes was significantly lower in humans (3.4%) compared to rats (26.3%), with two receptor classes (K1=1.4 nM, R1=0.06 pmol/mg; K2=10.8 nM, R2=0.22 pmol/mg).
- Insulin binding to the Golgi fraction showed a single class of receptors (Kd=5.6 nM, Ro=3.06 pmol/mg) and was half that of rats.
Conclusions:
- Human liver possesses distinct insulin and EGF receptor populations in microsomes and Golgi fractions.
- Lower EGF binding in human liver microsomes suggests potential species-specific differences in EGF signaling pathways.
- Further research is needed to elucidate the functional implications of these receptor differences.