Cross-linked polypentapeptide of elastin as a calcifiable matrix: Molecular weight dependence

The polypentapeptide, (L·Val¹-L·Pro²-Gly³-L·Val⁴-Gly⁵) _n , when cross-linked by γ-irradiation was shown to calcify when exposed to dialyzates of calcium and phosphate augmented fetal bovine sera and the molecular weight dependence of this calcification is investigated. Five molecular weight fractions, labeled I to V in order of increasing polymer size from under 12,000 dalton (I), that is, \(\bar n\) < 30, to over 100,000 daltons (V), that is, \(\bar n\) > 240, were γ-irradiation cross-linked at 10–12 MRAD to form matrices I–V. Calcium-45 was used to follow the time course and relative amount of calcium uptake from the sera. Scanning electron microscopy and electron probe microanalysis were used to characterize the extent of matrix calcification. All matrices took up calcium-45 from the sera; however, only matrices formed from polypentapeptide with \(\bar n\) greater than 100 calcified, that is, matrices III, IV, and V. Matrix V with \(\bar n\) > 240 calcified massively and in a manner comparable to chemically cross-linked polypentapeptide with \(\bar n\) ∼ 40 using nonaugmented sera. Presumably, γ-irradiation results in chain breakage. The γ-irradiation cross-linked matrices with values of \(\bar n\) ranging from under 30 to greater than 240 establish the molecular weight dependence of matrix calcification.