Krzywicki Revisited: Equations for Spectrophotometric Determination of Myoglobin Redox Forms in Aqueous Meat Extracts

ABSTRACT: Krzywicki's equations have been widely used for estimating the relative proportions of myoglobin (Mb) redox forms in aqueous solution. However, these equations have generated negative values for some redox forms, and total Mb estimates obtained by summation of the individual redox forms have deviated from unity. The inappropriate selection of wavelengths (545, 565, and 572 nm) used to generate these equations appears to have been responsible for these problems. Therefore, Krzywicki's equations were modified by using wavelength maxima at 503, 557, and 582 nm, representative for metmyoglobin, deoxymyoglobin, and oxymyoglobin, respectively. Millimolar extinction coefficients at these wavelengths were calculated, and a set of modified equations was established for determining the relative proportions of Mb redox forms in aqueous solution. The new equations demonstrated improved performance in decreasing the occurrence and magnitude of negative values and in estimating total Mb, when compared with Krzywicki' original equations.