Chromatographic assay reveals that the total amount of T 3 in the blood is 10 g.

Question

Chromatographic assay reveals that the total amount of T3 in the blood is 10 g. You find that the various bound forms of the hormone are:

T3(free) = 0.5%

T3 ~ albumin = 12 %

T3~TBG = 69 %

and T3~pro-albumin = 18.5 %

Target tissue: heart whose Bmax of T3 receptors = 76 fmol of T3 receptor/mg protein                    (1 fmol = 10-15 mol), where you have 100 g protein (total protein of which T3 receptors makes only a tiny fraction) in your heart assay. MW = 68 kDal = 68,000 g/mol [Dasmalopatra et al., Receptor, 2(4):213-223, 1992]. This reference is only for the MW of T3 receptor, and not for the solution to this question. Note: You won’t need the MW of T3 because you already have the amount in g.

Calculate the amount (in g) of available T3and its receptor (also in g). How do the 2 amounts compare? Will Bmaxbe reached?

Explanation / Answer

Free T3 constitute 0.5% of total T3 hormone. In blood, total amount of T3 is 10 g. The amount of available or free T3 is or 5 × 10-8 gm

Density or total concentration of T3 receptors is 76 fmol = 7.6 × 10-14 mol/ mg protein

Density of T3 receptors per 100 g protein is

Bmax can be calculated if binding potential of T3 is provided.

The question seems to be inappropriate, if Bmax is reached or KD is reached? KD is not reached as it required half of the Bmax to saturate the receptors

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