Ranges of low-energy electrons in protein.

Abstract

A KNOWLEDGE of the effective range of low-energy electrons in protein is of considerable biological interest. The ranges as calculated by Lea1 from the Bethe theory of energy-loss cannot be accepted without experimental verification, since the validity of the assumptions made in the computations are questionable at the low energies. The sensitivity of small biologically active molecules to radiation can be used to measure the ranges by employing a layer of enzyme of thickness greater than the range of the electrons as an absorber. If a thin, uniform layer of dry enzyme is irradiated with a sufficiently large number of electrons, all the enzyme within the range of electrons is inactivated. After irradiation, the enzyme is assayed for remaining activity; knowing the amount inactivated, the surface area irradiated and the density of the material (taken as 1.3 gm./c.c.)2 the range of the electrons in the enzyme can be found. Irradiations using the enzyme invertase3 have already been carried out, and the ranges found were significantly less than those calculated by Lea. The size of the enzyme molecule itself prevented any measurements being made at energies less than 600 eV., for at that energy a layer one enzyme molecule in thickness was inactivated. The inaccuracies of the assay made the determinations at energies greater than 1,500 eV. uncertain.