For a certain plasma or interstitial insulin concentration, which is the percentage of the human adipocyte insulin receptor bound to insulin? For instance, with a plasma insulin concentration of 150 pM which is the % of the cell receptors in the bound form? And which are the minimum and maximum percentages of the receptor in this form (e.g. could it be 0% or 100%: totally unbound or totally bound?).
Taking the value of 0.01 nM as the affinity (ref 1) the percentage of receptors in the bound form would be quite high: 94%.
I do not understand well your second question but the formula to calculate the % is
(100 * insulin in pM) = 10 pM + insulin in pM
If the affinity is not so low as 10 pM the percentages would decrease
(100 * insulin in pM) = affinity in pM + insulin in pM
In ref 2 affinity is reported to be 1 nM = 1000 pM
then the % would be 13%
Affinity is key. Probably 1 nM is closer to reality. Check also affinities of insulin binding to hepatocytes in ref 3 (table 1, range 0.53 to 0.97 nM)
ref 1
Correlations of Receptor Binding and Metabolic and Mitogenic Potencies of Insulin Analogs Designed for Clinical Use
Peter Kurtzhals, Lauge Schäffer, Anders Sørensen, Claus Kristensen, Ib Jonassen, Christoph Schmid, and Thomas Trüb
Ref 2
Fed Proc. 1975 Jun;34(7):1556-63.
Insulin: interaction with membrane receprots and relationship to cyclic purine nucleotides and cell growth.
Hollenberg MD, Cuatrecasas P.
Ref 3
Proc Natl Acad Sci U S A. 1980 Jun; 77(6): 3176–3180.
PMCID: PMC349577
REgulation of insulin binding to isolated hepatocytes: correction for bound hormone fragments linearizes Scatchard plots.
D B Donner
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