Structure and Reactivity of Transferrins

Unexplained Effects. Some observations are difficult to attribute to any of the freezing mechanisms considered so far. Most amenable to conceptual accommodation are those cases where a particular reactive intermediate, or a particular conformer, appears to have been trapped. This is believed to occur at very low temperatures where mobility at the atomic level is severely limited partly because of little thermal motion and partly because of the physical constraint provided by the glassy or icy structures of the medium. Normally unstable free radical derivatives of proteins can be studied by trapping them at low temperatures (e.g. 79). This technique also can be used to stabilize what appear to be specific conformational isomers of normal structures. For example, this approach has enabled the detection of an ammonia-catalase complex (80), conformers of the iron proteins conalbumin and transferrin (81), and a conformer of the flavoprotein L-amino acid oxidase (82, 83). 

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