ULTRASTRUCTURAL STUDIES OF HUMAN AND RABBIT αM-GLOBULINS

Electron micrographs of isolated human α(2)M-molecules, obtained by the negative contrast technique, revealed morphologically homogenous structures resembling a graceful monogram of the two letters H and I. The modal values for the length and width of the α(2)M particles were 170 A and 100 A, respectively. Purified rabbit αmacroglobulins contained about 80% α(1)M- and 20% α(2)M-globulins. The isolated rabbit α(1)M- and α(2)M-molecules were morphologically indistinguishable from one another and from human α(2)M-molecules. Preliminary immunoprecipitation studies demonstrated that the two rabbit αM-globulins were antigenically different. Sedimentation constant determinations gave s (20, w) values of 18.8 and 18.2 for rabbit α(1)M and α(2)M, respectively.