Aspects of calcification. The availability of ε-amino groups in collagen aggregates

Abstract

The free e -amino groups of 5 types of reconstituted collagen aggregate were determined by reaction with 1-fluoro-2,4-dinitrobenzene in aqueous media of various ionic strengths at pH 74 and 37[degree]. No significant differences existed between the e -amino group availabilities (approximately 61%) of the 640 A, 220 A and structureless aggregates on dinitrophenylation in 1% NaCl; although the availabilities of the fibrous long-spacing and segment long-spacing aggregates were appreciably lower (55%) in this medium. The [epsilon] -amino group availabilities of the 640 A, 220 A and structureless fibrils were also identical (69.5%) on dinitrophenylation at higher ionic strengths. When dinitrophenylated in water, the proportions of reactive [epsilon] -amino groups in the 640 A and the 2 long-spacing aggregates were considerably less (approximately 44%) than those of the same aggregates in l%NaCl. As the ionic strength of the aqueous dinitrophenylation medium was decreased, the molar ratio of lysyl to hydroxylysyl [epsilon] -amino groups available to fluorodinitrobenzene in the 640 A and the 2 long-spacing aggregates also decreased. Most samples of the fibrous long-spacing aggregate contained about 10% of the glycoprotein used in their preparation. These findings are discussed in relation to the calcification of collagen fibrils in-vitro.