<p dir="ltr">A schematic of the optical spectroscopy experimental preparation is shown in (<b>A</b>). The spectral properties of the LED used to illuminate the heart are shown in <b>B</b>. <b>C</b> and <b>D </b>demonstrate the average spectra of transmitted light through the heart, mean represented by the red and black lines shaded area represents the standard error of the mean. Data derived from (13-16) hearts. <b>E</b> shows the reference absorbance spectra for oxymyoglobin (MbO), deoxymyoglobin (MbD), and flavin adenine dicucleotide (FAD). <b>F</b> shows the reference difference spectra of the individual cytochromes of the electron transport chain. Reference spectra used here are derived from those described by Chess et al. (26). These reference spectra demonstrate that hearts are relatively transparent to light at 630 nm, arrow in panels E and F. Therefore, light at this wavelength was used to define an absorbance baseline, as shown in G and H. The blue lines in panels G and H show the portion of the spectrum used to fit changes in cytochrome absorbance during experimental protocols.</p>
