Abstract
It has now been thoroughly shown that under certain conditions the inorganic phosphate of the serum becomes incompletely diffusible. 1 A logical explanation of this phenomenon is that the non-diffusible phosphate which is formed is combined with some of the serum calcium in a compound which is in a colloidal state. As yet, no direct evidence is available as to the exact composition of this colloidal calcium phosphate.
On the basis of the view which has recently received strong support from the work of McLean and Hastings, 2 namely, that there is an equilibrium between the ionized and the protein bound calcium in serum which is governed by the mass law, it appears possible to develop a relationship which will quantitatively account for the partition of the serum calcium and one which will also yield a plausible value for the composition of the colloidal calcium phosphate. In the following treatment it is assumed that the diffusible calcium is virtually equivalent to the ionized calcium of the serum. This opinion also is supported by the work of McLean and Hastings.
For the present purpose, the mass law relationship may be conveniently written in the form,
where P represents the protein, CaP the calcium protein complex, and CaD ++ the diffusible calcium. A and B are constants whose significance is given below. The equation as given has the advantage that if the observed data obey the mass law, then a straight line is obtained on plotting the values of P/CaP against 1/CaD ++. The value of the constant A is given by the reciprocal of the point of intersection of the straight line on the P/CaP axis. It has the significance of being the maximum amount of calcium which can be bound by each unit weight of protein. The slope of the straight line gives the value of the constant B. This term consists of the equilibrium constant divided by A.
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