Respiration cellular, enzyme systems involved

Cyanide ion exerts an inhibitory action on certain metabolic enzyme systems, most notably cytochrome oxidase, the enzyme involved in the ultimate transfer of electrons to molecular oxygen. Because cytochrome oxidase is present in practically all cells that function under aerobic conditions, and because the cyanide ion diffuses easily to all parts of the body, cyanide quickly halts practically all cellular respiration. The venous blood of a patient dying of cyanide is bright red and resembles arterial blood because the tissues have not been able to utilize the oxygen brought to them. Cyanide intoxication produces lactic acidosis, the result of an increased rate of glycolysis and production of lactic acid. ... 

There are, however, many enzymes which, because they do not seem to be contained in such cellular particles, are referred to as soluble enzymes . Thus, the chemical reactions whereby the yeast cell converts glucose into ethanol and which seem to be identical with the first sequence of reactions in the normal respiration of plant cells are catalysed by such soluble enzymes. In the living cell such enzymes may, however, function as an organised multi-enzyme system which forms part of the endoplasmic reticulum. The fact that they cannot be obtained in association may merely reflect our inability to preserve the endoplasmic reticulum in cell-free preparations. Thus, in alcoholic fermentation by the yeast cell, which occurs in the absence of oxygen, there is an oxidative reaction which is balanced by a reduction. These both involve dehydrogenase enzymes having the same co-enzyme, nicotinamide adenine dinucleotide. One of these reactions, that catalysed by alcohol dehydrogenase, has already been mentioned (p. 73, eqn. 6). The other reaction... 

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