Studies on the Interaction of Carbon Monoxide with Tryptophan Oxygenase of Pseudomonas
Hiroo Maeno 1 and Philip Feigelson 1
From the
1 From the Departments of Biochemistry and Medicine, College of Physicians and Surgeons, Columbia University, New York, New York 10032
1. The inhibition of Pseudomonas tryptophan oxygenase by carbon monoxide is competitive with respect to oxygen and is photodissociable. The photochemical action spectrum, with a maximum at 421 mµ, is identical with the Soret absorption spectrum of the tryptophan-carboxyferroprotoporphyrin-enzyme complex. Thus both carbon monoxide and oxygen bind to the heme moiety of tryptophan oxygenase.
2. Equilibrium studies indicate that the affinity of carbon monoxide for the ferroprotoporphyrin of the enzyme is markedly enhanced by the presence of the substrate, tryptophan. The augmentation in binding of carbon monoxide to the enzyme is a sigmoidal function of the tryptophan concentration. 
-Methyltryptophan, a nonmetabolizable noninhibitory substrate analogue, which binds to an allosteric site on the enzyme, also enhances the affinity of the enzyme for carbon monoxide. The facilitation of carbon monoxide binding to the enzyme by the combined action of low levels of tryptophan and -methyltryptophan is synergistic, suggesting an interaction between the catalytic and allosteric sites.
3. Chemically reduced enzyme is only slowly reoxidized in the absence of tryptophan, without the spectral appearance of an oxygenated intermediary.
4. Freshly generated ferriprotoporphyrin enzyme is as catalytically active as ferroprotoporphyrin enzyme in both the absence and the presence of ascorbic acid.
Submitted on July 6, 1967
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