Effects of ionizing radiation on the amino acids of proteins and the reactivity of the protonated amino group depends upon the pK subscript a of the group. Estimates of the rate constants for reactions involving the amino acid side chains are presented. These rate constants gave an approximate rate constant for three different protein molecules

Braams, R.

English

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November 1968	 Brief 68-10424 
*tUV C
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the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Rate Constants Measured for Hydrated Electron 
Reactions with Peptides and Proteins 
is
The results of a study to measure absolute rate con-
stants for reactions between the hydrated electron and 
peptides or proteins have been documented by Reinier 
Braams of Argonne National Laboratory, Argonne, 
Illinois. This basic knowledge may contribute to the 
understanding of mechanisms of chemical changes in 
biological systems. 
In a protein, the amino acids are linked together 
through peptide bonds. Each protein molecule con-
tains a large number of these bonds. Therefore, it is of 
considerable importance to know if the peptide bond 
introduces a reactive site involved in reactions with 
the hydrate electron. It was established that the pep-
tide bond is not reactive toward the hydrated electron 
and that the reactivity of a problem can be ascribed 
to reactions with only a few specific amino acid side 
chains. 
In this study of the effects of ionizing radiation on 
the amino acids of proteins, the reactivity of the pro-
tonated amino group is shown to depend upon the 
P K a of the group. Estimates of the rate constants for 
reactions involving the amino acid side chains are pre-
sented. From the estimated rate constants for the side 
chains, an approximate rate constant for three dif-
ferent protein molecules has been calculated. In the 
linear gelatin molecule, the calculated value agrees 
well with the experimental value. For the ribonuclease 
and lysozyme, however, the calculated values differ 
from the measured values. The differences are ascribed 
to the influence of the protein charge on the encounter 
frequency, and to the effect of folding of the peptide 
chain on the effective collision radius of the molecule. 
The proteins investigated have shown a high reac-
tivity toward the hydrated electron. In order to
measure the absolute rate constants, low molar con-
centrations and small electron pulses were necessary. 
For this reason, the experiments were carried out with 
a multiple pass cell, allowing the analyzing light beam 
to pass through the radiation cell several times. 
Usually, eight passes were made, giving an optical 
path length of 32 cm in the protein solution. The radi-
ation dose of 0.4-Msec pulse was of the order of 500 
rad and produced about I .5 tiM of hydrated electrons. 
In some experiments with gelatin, the molar concen-
tration was smaller than the initial concentration of 
hydrated electrons after one single pulse. The rate 
constant was then obtained from the initial slope of 
the decay curve after the first single pulse. 
Notes: 
I. A paper, entitled "Rate Constants of Hydrated 
Electron Reactions with Peptides and Proteins," 
Radiation Research, volume 31, no. 1, pp. 8-26. 
May 1967, Academic Press Inc., presents and an-
alyzes the results of these measurements. 
2. This work is of a fundamental nature and may be 
of interest to cell physiologists, medical re-
searchers, biochemists, and biophysicists. 
3. Inquiries concerning this innovation may be di-
rected to:
Office of Industrial Cooperation 
Argonne National Laboratory 
9700 South Cass Avenue 
Argonne, Illinois 60439 
Reference: B68-10424
Source: R. Braams

of the Chemistry Division

(ARG-10195) 
(continued overleaf) 
This document was prepared under the sponsorship of the Atomic 	 liability resulting from the use of the information contained in this 
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Administration. Neither the United States Government nor any per-
	 method, or process disclosed in this document may not infringe pri-
son acting on behalf of the United States Government assumes any
	 vately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19680000424 2020-03-12T06:01:53+00:00Z
Patent status: 
Inquiries about obtaining rights for commercial use 
of this innovation may be made to: 
Mr. George H. Lee, Chief 
Chicago Patent Group 
U.S. Atomic Energy Commission 
Chicago Operations Office 
9800 South Cass Avenue 
Argonne, Illinois 60439 
Brief 68-10424	 Category 04


Rate constants measured for hydrated electron reactions with peptides and proteins

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