Bacterial cytochromes; difference spectra

Methods have been devised for handling suspensions of intact bacteria so that the difference spectra (difference between the reduced and the oxidized forms) of the cytochromes can be measured using special spectrophotometric techniques. These spectra establish the positions of the cytochrome peaks and also allow some quantitative measurements concerning the bacterial cytochromes.Several kinds of bacteria showed spectra with cytochrome peaks in the same positions as those of yeast and heart muscle. In some bacteria the peak corresponding to cytochrome a was missing; this was usually, but not always, replaced by either cytochrome a₁ or by a mixture of cytochromes a₁ and a₂. Cytochrome b or b₁ was present in many bacteria, as well as a pigment with a peak at 552 mμ and one with a maximum at 554 mμ. The latter pigment has not been described previously. A number of different combinations of the various cytochromes were observed in the group of bacteria studied.Cytochrome a₂ appears to have very little absorption in the Soret region of the spectrum.Calculations of the relationship of the increase in optical density on reduction to the turbidity show that for spectrophotometric methods, most bacteria are easier to work with than is yeast.The respiration rates of the bacteria, expressed on the basis of dry weight or turbidity, vary considerably. When the respiration is expressed in terms of the cytochromes present, it is found that some of the bacterial systems are considerably more active (have higher turnover numbers) than that of yeast or heart muscle. The cytochrome systems of the two strains of acetobacter have particularly large turnover numbers.Calculations of the ratios of the Soret peaks to the peaks in the visible region of the spectrum show a number of differences among bacteria which seem to contain similar cytochrome components.