A completely optical method was developed for evaluating myoglobin-oxygen saturation. Solution oxygen concentrations were computed from measurements of phosphorescence decay of a soluble palladium porphyrin according to the Stern-Volmer quenching relationship. Visible absorption spectra were recorded of myoglobin solutions progressively deoxygenated by bacterial aerobic metabolism. Myoglobin oxygenation curves were obtained from the spectra by two full-spectrum procedures, singular value decomposition (SVD) and curve fitting, and by the traditional dual-wavelength isosbestic method. The calculated P<sub>50</sub> for horse heart myoglobin at 24 ± 1°C was 1.2 Torr by SVD, 1.2 Torr by curve fitting, and 1.4 Torr by dual-wavelength spectroscopy. These results compare favorably with a value of 1.1 Torr estimated from the work of Rossi-Fanelli and Antonini for human myoglobin. The Hill coefficient, theoretically 1.00 for myoglobin, was experimentally determined to be 0.96 by SVD and 0.95 by curve fitting of the spectral data matrix.
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