Substrates and Intermediates in the Enzymatic Reduction of Metmyoglobin in Ground Beef

SUMMARY– Various substrates were tested for their ability to increase the reduction of metmyoglobin by donating electrons to NAD. Intermediates of the glycolytic pathway which proved to be effective were glyceraldehyde‐3‐phosphate and fructose‐1, 6‐diphosphate. Other substrates, oxidized by NAD‐linked dehydrogenases known to be present in meat are a‐glycerophosphate, malate and glutamate. These also increased metmyoglobin reduction when added to meat. The pathway of electron transport from NADH to metmyoglobin is believed to be mainly by way of DT diaphorase (menadione reductase) and quinones, since dicumarol, a specific inhibitor of this enzyme, partially blocked the reaction in meat. Higher levels of quinones did not accelerate the reaction.