The Effects of Added Agar on the Radiation Sensitivity of Trypsin in Solution

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Abstract
Mixtures of trypsin (0. 7 to 5 [mu] M) and agar (0. 001 to 0. 005%) were irradiated with 250-kvp X-rays at 4[degree]C to investigate further the inactivation of an enzyme in a heterogeneous system which may simulate some cellular conditions. Even in such a relatively simple system, 3 classes of trypsin molecules with widely differing properties can be demonstrated (1) Some molecules require inactivation doses only slightly larger than those for trypsin in solution alone; (2) another class of molecules has a greatly decreased radiation sensitivity; and (3) some trypsin activity is lost completely during mixing. The occurrence of trypsin-agar complexes can be readily inferred from the appearance of "scattering" spectra which are monotonically correlated with concentration. A number of factors, such as the order of mixing, the time of mixing, and the method of assay, influences the extent of class 2 and class 3 molecules. These results raise important questions concerning the relevance of studies in model systems to an understanding of radiobiological mechanisms in cells.

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