title: Johns Hopkins University, Baltimore, Maryland.
abstract: The STEM can be used in one of three modes: 1) to image individual atoms; 2) to measure mass or molecular weight; 3) to collect electron energy loss spectra or x-ray fluorescence data. Heavy atom imaging is used to identify chemical groups in a molecule or macromolecules in an assembly. Specific labels have been developed for bases in nucleic acids. These permit localization of bound proteins on single strand nucleic acids. Pt(gly-L-met)Cl is a specific label for methionine residues of proteins as shown with the SLS aggregate of collagen. Lysine can be labeled as well if first methyl (methyl-thio-acetimidate) is coupled. This labeling procedure permits the localization of individual histones within a nucleosome. Mass determination can be used to answer crucial questions about biological assemblies. This is demonstrated by examples from muscle structure.
mesh_terms: D000596:Amino Acids; D001483:Base Sequence; D001665:Binding Sites; D055598:Chemical Phenomena; D002621:Chemistry; D003094:Collagen / Q000032:analysis; D004247:DNA / Q000032:analysis*; D006657:Histones / Q000032:analysis; D008855:Microscopy, Electron, Scanning / Q000379:methods*; D009707:Nucleosomes / Q000032:analysis; D009944:Organoplatinum Compounds; D011506:Proteins / Q000032:analysis*; D012313:RNA / Q000032:analysis*
chemical_list: D000596:Amino Acids; D006657:Histones; D009707:Nucleosomes; D009944:Organoplatinum Compounds; D011506:Proteins; C034861:chloroglycyl-methionatoplatinum II; D012313:RNA; D003094:Collagen; D004247:DNA