64 L. A. BLUMENFELD AND A. E. KALMANSON 



(n) In the ESR spectra of irradiated native proteins and lyopliilized 

 tissues (60 to 80 per cent of proteins) two special features may be dis- 

 cerned. First, the number of free radicals produced in proteins and 

 tissues is from one to three orders of magnitude less than in amino acids 

 and peptides (with equal doses of y-irradiation). Second, the signal is 

 not a superposition of ESR specti'al patterns (this might be expected 

 since the energy of y-quanta is quite sufficient to break any peptide 

 bonds in proteins), but is usually a single naiTow peak with a half- width 

 of 4 to 10 oersted and without any hyperfine structure. 



The position and the width of the signal is usually the same as that 

 for ESR spectra of enzyme specimens frozen and lyopliilized at the 

 moment the enzyme action takes jjlace. The narrowness of the signals 

 cannot be explained by exchange interactions, because of the small 

 concentration of unpaired electrons. We must admit a translational 

 mechanism for the narrowing (Anderson 1954). 



The small intensity of signals in irradiated proteins and the absence 

 of hyperfine structure, in comparison with signals from iiTadiated 

 amino acids, are of si3ecial interest to radiobiologists. 



In the case of irradiated amino acids and peptides the ESR signal is 

 due to "holes" with unpaired electrons, or to neutral free radicals 

 arising when bonds are broken homogeneously. 



However, from the point of view of our hypothesis about the exis- 

 tence of energy levels of a molecule as a whole or, as we called them, 

 "conductive channels", it may be suggested that in native proteins 

 eliminated electrons can re-enter the previously mentioned "bands", 

 formed by an orderly net of hj^drogen bonds, and return along them to 

 the "holes", recombining with them and "healing" the injuries. 



This hyx^othesis about the role of regular hydrogen bonds in creating 

 "conductive bands" and in increasing the radio -resistance of proteins, 

 was investigated in special expei'iments. 



It is known that heat denaturation sharply disturbs an orderly 

 system of hydrogen bonds, and makes it chaotic. When denaturation is 

 sufficiently complete proteins lose their biological activity completely. 

 A number of protein prej^arations were exposed to heat denaturation 

 before lyophilization and irradiation. In all cases intense signals were 

 obtained with clearly expressed hyperfine structure, characteristic of 

 free radicals with localized electrons, instead of a weak narrow singlet. 

 By increasing the amount of denaturation, an increase of radical yield 

 by one to three oixlers was produced. 



We suppose that the disturbance of the secondary structure of 

 protein molecules during the denaturation leads to the disappearance 

 of "conductive channels" along which the electrons ejected by the 



