Abstract
Oxidation-reduction systems which are extremely positive from a biological point of view are continually circulating in the animal organism, but the poising effects of the redox systems of middle range such as hemoglobin are so efficient that the effects of these positive systems formed as intermediate products in the metabolism of phenyl alanine and tyrosine components of protein pass unnoticed. Only in pathological states, such as alkaptonuria, with its accompanying ochronosis, in cases of poisoning with overdosage of acetanilid, aniline, benzene, phenol, etc., can they be appreciated.
We have measured the oxidation-reduction potential of homogentisic-benzoquinone acetic acid as representative of these systems and as a substance known to circulate in the blood in alkaptonuria. This was done with bright platinum electrodes in strongly buffered solutions at fixed temperature of 25° with exclusion of air above pH 3. Table I is typical of the results. Quinone-hydroquinone was measured in the same way. Graph 1 shows the relation of pH and Eh of these systems, and for purposes of orientation hemoglobin-methemoglobin as measured by Conant 2 is included in the graph.
It has been shown by the work of Küster 1 and Conant 2 that the iron in methemoglobin is in the ferric state contrasted to the ferrous iron present in hemoglobin and oxyhemoglobin. The potential of the hemoglobin system is 0.15 V at body pH. Graph 1 shows that the potential of the strongly positive systems are all above 0.25 Volts at body pH. In poisoning by aromatic substances circulation of polyhydroxylated phenols causes a shift in the hemo-globin-methemoglobin equilibrium in favor of methemoglobin. This is the characteristic symptom of poisoning by these agents.
The injection of acetanilid, resorcinol, etc., into dogs results in the formation of as much as 50% methemoglobin.
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