3-DIMENSIONAL IMMUNOELECTRON MICROSCOPY OF SCORPION HEMOCYANIN LABELED WITH A MONOCLONAL FAB FRAGMENT

An immunocomplex of the 4 x 6-meric hemocyanin of the scorpion Androct onus australis with the monoclonal Fab fragment L104 was reconstructed from electron micrographs of a negatively stained specimen, using the double-carbon-layer technique. The resulting structure enables a clea r visualization of the Fab fragments bound to the four copies of the A a6 subunit and directly confirms a previous localization of the L104 e pitope deduced from two-dimensional image processing. Despite a strong flattening effect produced by the negative-staining technique the ori entations of the Fab fragments are well characterized. Moreover, the o bservation of a central hole within the elbow bends of the Fab fragmen ts provides information about the disposition of the Fabs around their main axis. (C) 1993 Academic Press, Inc.