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Abstract A three-dimensional electron density map has been calculated at 6 Å resolution for a human γG1 immunoglobulin molecule. X-ray diffraction data have been collected for the native protein crystals and for three heavy atom derivatives prepared by soaking the crystals in PCMBS, Hg(CN)2 and PtCl6-. Three distinct globular regions have been identified in the electron density map. One of these surrounds the molecular dyad axis and has been interpreted to be the Fc fragment. The other two regions are identical to one another and have been interpreted to be the Fab fragments. There are four ways of joining these globular regions of electron density to make a complete molecule and these lead to four possible models of which a T-shaped model is favored. The dimensions of this model compare extremely well with those reported by other physical and chemical techniques for immunoglobulin molecules.
Sarma et al. (1971) studied this question.