title: Shadowing of elongated helical molecules (myosin, tropomyosin, collagen, and DNA) yields regular molecule-dependent heavy metal grain patterns.
abstract: Myosin and other alpha-helical molecules (tropomyosin, collagen) can now directly be adsorbed on EM support films, washed, air-dried, or frozen and freeze-dried. Using this method, the molecules were rotary or unidirectionally shadowed with different heavy metals (Pt/C, Ta/W, Ag) or with C alone. After shadowing at low elevation angles with Ta/W or Ag, myosin, tropomyosin, collagen, and DNA showed strikingly regular patterns of either single or coalesced heavy metal grains (bands) along their entire lengths. Even after shadowing with C alone, repetitive, granular accumulations or bands of C were found along the molecules. The different heavy metals and C displayed distinctive banding patterns on the molecules examined, all of which are characterized by different surface charge periodicities and pitch values. The patterns were quantified on the basis of the distances between grains or bands. Two most frequently measured distances between bands were found after shadowing with heavy metals. After shadowing with Ag the prevalent distances between grains were about twice as large as those after Ta/W shadowing. By evaporating a thin layer of carbon on the molecules before shadowing with heavy metals or by evaporating C alone (with no heavy metal) at 6 degrees, one of these two most prevalent distances between bands was attenuated or disappeared. It was demonstrated that the remaining most frequently measured distances between grains seemed to be related to relief periodicities, to the pitch of the double-coiled (myosin, tropomyosin) and triple-coiled alpha-helices (collagen) and fractions thereof. The attenuated distances between grains agreed very well with distances of periodic surface charges on the molecules examined. The investigation of the grain or band patterns showed that their characteristics appearance was molecule-dependent and caused both by periodic chemical (repeats of positive and negative surface charges) and periodic structural features (coiling of the helical strands). The examination confirmed the existence of periodic positive and negative surface charges along the myosin rod and suggested a value of about 17.0 nm for the hitherto undetermined pitch of the double-coiled myosin rod.
mesh_terms: D000818:Animals; D002417:Cattle; D002645:Chickens; D003094:Collagen; D004275:DNA, Ribosomal; D004023:Dictyostelium; D005612:Freeze Drying; D008854:Microscopy, Electron; D009132:Muscles; D009218:Myosins; D009690:Nucleic Acid Conformation; D011487:Protein Conformation; D012867:Skin; D014335:Tropomyosin
chemical_list: D004275:DNA, Ribosomal; D014335:Tropomyosin; D003094:Collagen; D009218:Myosins