radiation inactivation method

a technique, based on target theory, that enables the size of the functional unit of a biologically active macromolecule (or of its complexes with other molecules) to be estimated; it can be used on unpurified (e.g. membrane-bound) material. Determinations are made of the biological activity remaining in a sample after exposure to various large doses of ionizing radiation (electrons or X- or gamma radiation of at least 1 MeV), and the value, D₃₇, of the radiation dose, expressed in Mrad, required to reduce the activity to 37% of (i.e. e⁻¹ times) its original value is obtained; the relative molecular mass, M_r, of such a macromolecule may then be found from the empirical relationship M_r = 6.4 × 10⁵/D₃₇, where D₃₇ is determined at 30°C.

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