National Registry in Clinical Chemistry

Recently we had occasion to assay for lactate dehydrogenase (EC 1.1.1.27) in the presence of a large amount of potassium cyanide and were surprised to see a 10-fold increase in the enzyme activity when we used a method that depends on the measurement of NADH. At first we thought that we had made a significant observation.You can imagine our disappointment when we found that a control consisting of isotonic saline gave similar results, indicating that this was a reaction between the NAD and cyanide. Ultimately Dr. Albert A. Diets brought to our attention a reference describing this phenomenon (1). This Letter is for the benefit of others who may be similarly deluded, primarily those who may be involved in investigating the biochemical effects of cyanide. Interestingly enough, we found one reference that stated that cyanide abolishes the inhibitory effect of certain enzyme inhibitors (2). Possibly this phenomena may also occur in patients with cyanide poisoning, although we are not aware of it having been described in the literature.