The two components of spectrin, filamin, and the heavy chain of smooth muscle myosin show no detectable homologies to one another by two-dimensional mapping of iodinated tryptic peptides.

The possible structural relationships among four high molecular weight mechanochemical proteins has been examined using two-dimensional mapping of the tryptic peptide fragments prepared from ¹²⁵I-labeled proteins (Elder et al., J. Biol. Chem. $\text{252}$:6510–6515 (1977)). Erythrocyte spectrin bands 1 and 2 protein, the heavy chain of smooth muscle (uterine) myosin, a filamin from human and rabbit were studied. The maps of the four proteins within each species differed considerably from each other, with no apparent homologies evident among them, whereas maps of the same individual protein between the two species showed a high degree of homology.