The Radiation Sensitivity and Molecular Weight of Dry β-Galactosidase

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Abstract
Irradiation of dry preparations of Escherichia coli adapted to lactose, with Co60 gamma-rays, deuterons, and [alpha]-particles, leads to a measured sensitive volume of 4.26 X 10-19 cc, an area of 7.2 X 10-13 cm2, and an effective thickness of 5.3 X 10-7 cm. These figures support the idea of a spherical molecule of radius 47 A and molecular weight 330,000. Sedimentation measurements indicate a spread in constants averaging 19 Svedberg units. Irradiation by cobalt gamma-radiation in wet C minimal medium gave a slightly higher sensitive volume of equivalent molecular weight 500,000. The insensitivity to radicals produced in water may be due to the enzyme''s being protected in a membrane or by its own folding.

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