Hemoglobin and Cyanide

Bob Hoesch Bob_Hoesch at fws.gov
Tue Dec 5 13:30:52 EST 1995


Bob Hoesch Wrote:
>>>If one is using hemoglobin as a marker for analyzing population   
>>>genetics, a standard procedure is to treat the blood sample with low 
>>>concentrations of cyanide prior to IEF (isoelectric focusing).  This 
>>>results in the elimination of "spurious" bands, and apparently makes    
>>>the resulting banding patterns amenable to genetic analysis. I've heard    
>>>this procedure described as "reduction of methemoglobin" (reduction of     
>>>the oxidized iron back to the reduced state), but this doesn't make sense 
>>>to me in terms of the chemistry. Can someone explain what is happening in 
>>>this cyanide-induced reduction in the number of hemoglobin bands?  How 
>>>could cyanide reduce Fe3+ to Fe2+?  

???wrote 
>> It doesn't.  Methemoglobin forms a tight complex with CN, and ordinary Hb 
>> doesn't.  Presumably this affects the absorption bands enough to eliminate 
>> them as interference.  One of the treatments for HCN poisoning is to
>inhale an 
>> organic nitrite, which oxidizes Hb to mHb.  The CN is then tied up by the mHb 
>> instead of trashing the cytochroma oxidase, which is its toxic target.

Doug Yanega wrote:
>This raises a question: I've been told by a colleague that cyanide builds
>up in the body tissues over time, and that after years of slight sublethal
>doses, one more tiny dose can "push a person over the edge" suddenly. This
>was part of his mandatory education working in an analytical chemistry lab
>some 40 years ago. This seems completely at odds with my understanding of
>the chemistry involved in cyanide toxicity, and I'm curious as to whether
>this is at all possible - I'm a professional entomologist, and am exposed
>to sublethal doses of cyanide hundreds of times a year.....

Hoesch writes again:
Two comments.  

1)  If cyanide preferentially binds to metHb, how would this affect 
the electrophoretic pattern?  In practice, one sees a reduction in the number 
of Hb bands. Could the binding of one CN- per molecule knock the pI of the 
resulting complex completely out of the gradient? (This is the only thing I 
can think of)

2) Doug, I've never heard of "cumulative cyanide toxicity" and it doesn't make 
sense to me either.  Cyanide is very water soluble and would tend to be 
excreted.  And if it does bind irreversibly to metHb, the mean lifetime of red 
blood cells is only something like 120 days, after which they are taken out of 
circulation.  At that point the cyanide should be released and excreted. 

Bob Hoesch
U.S. Fish & Wildlife Forensics Lab





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