Reaction of the hydrated electron with amino acids, peptides, and proteins in aqueous solutions

Journal Article · Mon Aug 01 04:00:00 EDT 1977 · Radiat. Res.; (United States)

DOI:https://doi.org/10.2307/3574675· OSTI ID:7211840

Faraggi, M ^[1]; Bettelheim, A

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1. Ohio State Univ., Columbus

The reaction rate constants of e/sup -//sub aq/ with glycyl-histidine (Gly-His) and ..beta..-alanylhistidine (Carnosine, ..beta..-Ala-His) were determined and compared to those of ..beta..-alanylalanine (..beta..-Ala-Ala), alanyl-alanine ((Ala)/sub 2/), and histidine (His). The rate constants were found to be pH dependent. Below the pK value of the imidazole ring, the rate constants of the histidyl peptides are similar to that of His. This indicates that the main site of the e/sup -//sub aq/ reaction is the protonated ring. Above this pK value the pH dependent rate constants were less in the His amino acids than in the His peptides. This difference was attributed to the presence of the carbonyl grup in the peptides. This group, which is known to react quite rapidly with e/sup -//sub aq/, exhibits its presence when the imidazole ring loses its reactivity after deprotonation. The difference in reactivity toward e/sup -//sub aq/ between the ..cap alpha.. and ..beta.. His peptides is explained by the relative position of the protonated amino groups with respect to the carbonyl groups. A similar difference was also found in (Ala)/sub 2/ and ..beta..-Ala-Ala. The transient absorption spectra resulting from the reaction of e/sup -//sub aq/ with the His peptides were recorded and examined with respect to peptide concentration and pH dependence. Here again, at pH values below the pK of the imidazole, the transient absorption spectra are similar to that of histidine. In alkaline solutions, however, proper experimental conditions could be attained only for Gly-His. In His and ..beta..-Ala-His the interference of the OH radical reaction was observed. In Gly/sup -/His it was found that the band characterizing the imidazole transient (lambda/sub max/ = 360 nm) disappears with a simultaneous appearance of a band at lambda/sub max/ similarly ordered 410 nm.

• OSTI ID: 7211840
• Journal Information: Radiat. Res.; (United States), Journal Name: Radiat. Res.; (United States) Vol. 71:2; ISSN RAREA
• Country of Publication: United States
• Language: English

Related Subjects

550200* -- Biochemistry
59 BASIC BIOLOGICAL SCIENCES
ALANINES
AMINO ACIDS
AQUEOUS SOLUTIONS
AZOLES
BIOCHEMICAL REACTION KINETICS
CARBOXYLIC ACIDS
CHEMICAL RADIATION EFFECTS
CHEMICAL REACTIONS
CHEMISTRY
DECOMPOSITION
DISPERSIONS
ELECTRONS
ELEMENTARY PARTICLES
FERMIONS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HISTIDINE
IMIDAZOLES
KINETICS
LEPTONS
MIXTURES
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PEPTIDES
PH VALUE
PROTEINS
RADIATION CHEMISTRY
RADIATION EFFECTS
RADIOLYSIS
REACTION KINETICS
SOLUTIONS
SPECTRA