Oxidation of haemoglobin by oxygen in light: possible role of singlet oxygen

In vitro and in vivo ultraviolet-induced alterations of oxy- and deoxyhemoglobin

Ultraviolet (UV) radiation was found to convert oxyhemoglobin and deoxyhemoglobin stoichiometrically into methemoglobin and a met-like product, respectively. The peak conversion efficiency for oxyhemoglobin occurred at 285 nm and decreased by a factor of 100 by 315 nm. The peak conversion efficiency for deoxyhemoglobin occurred at 290 nm and decreased by a factor of 30 by 320 nm. The transformation of oxyhemoglobin to methemoglobin was also documented in intact erythrocytes using UV-B radiation. Finally, similar transformations were found to occur in human skin with UV-B exposure but not on all volunteers tested. These results imply that methemoglobin will be formed in vivo on solar exposure and provide evidence that UV-B photons reach the blood vessels.

N-hydroxy-N-arylacetamides--IV. Differences in the mechanism of haemoglobin oxidation in vitro between N-hydroxy-N-arylacetamides and arylhydroxylamines

In solutions of purified human haemoglobin N-hydroxy-4-chloroacetanilide (N-hydroxy-4ClAA] was one of the most active compounds and N-hydroxy-acetanilide (N-hydroxy-AA) was the least active compound among the six N-hydroxy-N-arylacetamides tested for ferrihaemoglobin (HbFe3+)-forming activity. Co-oxidation of haemoglobin by N-hydroxy-4-chloroacetanilide was compared with that of N-hydroxy-4-chloroaniline(N-hydroxy-4ClA) and found to differ in the kinetics of HbFe2+-oxidation, in the catalytic activity of the two compounds, in the activation energy, and in the product pattern, indicating that the mechanism by which N-hydroxy-N-arylacetamides oxidize oxyhaemoglobin in vitro is different from that of arylhydroxylamines. Attempts have failed to detect by EPR spectroscopy acetyl 4-chlorophenyl nitroxide radical, the postulated catalytically-active oxidation product of N-hydroxy-4-chloroacetanilide.

Free radical initiation in proteins and amino acids by ionizing and ultraviolet radiations and lipid oxidation--Part 22: ultraviolet radiation and photolysis

Parallels and similarities in chemical and functional damage to proteins by ionizing and UV radiations and oxidizing lipids have been recognized for some time. However, only recently have oxidizing lipids been shown directly by electron spin resonance to be radiomimetic also in their capacity for protein free radical production. Free radicals play a key role in the transformation of energy to molecular and cellular damage. It is thus of critical importance to elucidate the general mechanisms of free radical formation and reactions in proteins in order to understand protein involvement in various pathological conditions and in food deterioration. Accordingly, this review is a detailed comparison of gamma radiation, UV radiation, and lipid oxidation for what is presently known concerning (1) the specific modes of energy deposition and free radical formation, (2) the free radicals formed in proteins and amino acids, and (3) the typical damage correlating with these radicals.