Hemoglobin reduction systems

A number of copper -containing protein compounds are enzymes with an oxidase function (ascorbic acid oxidase, urease, etc 1 and these play an important role in Ihe biological oxidation-reduction system. There is a definite relationship of copper with iron in connection with utilization of iron in hemoglobin function. 

Nitrosoarenes are readily formed by the oxidation of primary N-hydroxy arylamines and several mechanisms appear to be involved. These include 1) the metal-catalyzed oxidation/reduction to nitrosoarenes, azoxyarenes and arylamines (144) 2) the 02-dependent, metal-catalyzed oxidation to nitrosoarenes (145) 3) the 02-dependent, hemoglobin-mediated co-oxidation to nitrosoarenes and methe-moglobin (146) and 4) the 0 2-dependent conversion of N-hydroxy arylamines to nitrosoarenes, nitrosophenols and nitroarenes (147,148). Each of these processes can involve intermediate nitroxide radicals, superoxide anion radicals, hydrogen peroxide and hydroxyl radicals, all of which have been observed in model systems (149,151). Although these radicals are electrophilic and have been suggested to result in DNA damage (151,152), a causal relationship has not yet been established. Nitrosoarenes, on the other hand, are readily formed in in vitro metabolic incubations (2,153) and have been shown to react covalently with lipids (154), proteins (28,155) and GSH (17,156-159). Nitrosoarenes are also readily reduced to N-hydroxy arylamines by ascorbic acid (17,160) and by reduced pyridine nucleotides (9,161). 

Furthermore, an increased oxidation rate of Hb—the reduction capacity remaining normal—will result in methemoglobinemia (H23, K13, K20). By this, two essentially different forms of methemoglobinemia can occur (a) deficiency in MHb reducing system and (b) acceleration of Hb oxidation. The question, whether or not the latter form of methemoglobinemia is identical with the so-called hemoglobin-M disease must be clarified by futher investigations. As yet, abnormal spectra of Hb as well as of MHb have been reported in such cases (H23, K13, K20, P3). 

At relatively low concentrations, lead produces relatively modest or short-term effects, including elevation of blood pressure, reduction in the synthesis of hemoglobin, and decreased ability to utilize vitamin D and calcium. With increased blood concentrations of lead, however, these problems become more severe. Impairment of the central nervous system can occur, with decreased mental functioning and hearing damage as two possible results. At very high lead concentrations, a person can fall into a coma and, eventually, die. 

Nitrogen tetraoxide is absorbed through the respiratory system and reacts with blood, reducing fluid levels, inducing massive pulmonary edema, and a severe reduction in hemoglobin levels. 

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