THE PARTITION AND BINDING OF CALCIUM IN THE SERUM OF THE LAYING HEN AND OF THE ESTROGENIZED ROOSTER1

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Abstract
Total calcium of serum was increased in roosters from a normal value of 10 mg per cent to 100 mg. per cent or higher at about 5 days following an injection of 125 mg of estrogenic substance (Ayerst). With this tenfold increase in the total serum calcium, there was a pari passu appearance and increase in concentration of a phosphoprotein complex, found normally in the serum of the laying hen, but not found, under usual conditions, in the serum of the rooster. This included two specialized proteins, X1 (a phosphoprotein) and X2 (a phospholipid lipoprotein). Chylomicrons and beta-lipoproteins were increased and alpha lipoproteins were decreased in concentration at the same time. When the total calcium was elevated to 100 mg. per cent, beta lipoproteins appeared to bind approximately 10 mg per cent; albumin 5 mg per cent; and X1 and X2 (chiefly X1) 79 mg. per cent. Only approximately 6 mg per cent of the total serum calcium in both control and estrogenized roosters was present in ultrafilterable form. Since the ultrafilterable fraction of the serum calcium did not change during the rapid and dramatic rise of the total calcium, it follows that the added calcium was entirely in the nondiffusible fraction. Moreover, from the evidence of the ultracentrifuge, the major portion of the increase in non-filterable calcium was held in an undissociated complex with the phosphoprotein. There was no evidence for the presence of a colloidal calcium phosphate complex. Calculations have been made of the capacity of the mixed serum proteins of the estrogenized fowl for the binding of calcium, and these proteins were found to have a much greater capacity, per unit weight, for combining with calcium than any other protein, including casein, previously studied. On the other hand, when the dissociation constant of the calcium-protein complex was calculated, it did not appear to be markedly different from that of other proteins, indicating that the affinity for calcium was essentially the same. The phosphoprotein fraction was deposited in the granules of egg yolk, in the laying hens studied, with the full complement of calcium with which it was associated in the serum.