Modulation of the epsilon-(gamma-glutamic)lysine cross-link in cellular proteins. II. Fractionation studies

The epsilon-(gamma-glutamic)lysine cross-link content of glycerol-extracted cultured embryonic chick heart myofibrils is increased by treatment with Mg2+-ATP followed by Ca2+ but not by Ca2+ alone. Fractionation of protein chains dissolved in sodium dodecyl sulfate and dithiothreitol shows that the increase of cross-link content occurs in very large proteins (greater than 250 kdaltons) and that there is a very marked decrease in cross-link content in the 82 kdalton region. Treatment of the glycerol-extracted myofibrils with Mg2+-ATP followed by Ca2+ also increases the amount of protein in the very high molecular weight fraction and there is a corresponding reduction of material in some of the lighter chains particularly in fibronectin, actin and in 82 and 51 kdalton chains. The relevance of Mg2+-ATP plus Ca2+ -dependent Glu-Lys cross-link formation to cyclical or reversible cellular processes is discussed briefly.