Alterations of gammacarboxyglutamic acid in formic acid and guanidine extracts in phosphate-deficient rat bone

We developed rickets and osteomalacia in rats by means of a low phosphorus, normal calcium and normal vitamin D diet, causing severely inhibited mineralization. The concentrations of gammacarboxyglutamic acid (Gla) in 10% formic acid and 5M guanidine extracts were studied in normal and phosphate-deficient rat bone. Although the Gla concentration in the formic acid extract was constant for both groups, it decreased in the guanidine extract of the phosphate-deficient group. The Gla content of the guanidine extract reflected a lower concentration of Gla-containing proteins, one of which, matrix Gla protein (MGP), acts as a mineral deposition inhibitor. Thus, the production of MGP decreased in the impaired mineralization of bone. The quantification of Gla in formic acid and guanidine extract is useful in studying the Gla-containing proteins, osteocalcin and MGP.