Cytochrome b /// the Respiratory Chain 



577 



tentative conclusions which we draw from the results obtained by ourselves, 

 and by Chance. 



PIGMENTS PRESENT IN HEART-MUSCLE PREPARATION, 



WHICH ABSORB IN THE SAME REGION OF THE SPECTRUM 



AS CYTOCHROME b 



Oxymyoglobin and Myoglobin 



Colpa-Boonstra and Minnaert (1959) have shown that even carefully 

 washed heart-muscle preparations contain sufficient oxymyoglobin to cause 



420 440 



Wovelength, 



m/u 



Fig. 1. Demonstration of myoglobin in heart-muscle preparation. Difference 

 spectra: (CO-compounds minus deoxygenated). A, normal heart-muscle 

 preparation; B, idem, after tipping in myoglobin; C, idem, after tipping in 

 haemoglobin; D, heart-muscle preparation treated with NaNOa- Light path, 

 1cm. Normal heart-muscle preparation, 1-16 mg protein/ml; NaNOg-treated 

 preparation, 1-56 mg protein/rnl. (From Colpa-Boonstra and Minnaert, 1959.) 



interference in measurements of cytochrome b. This pigment was identified 

 by an accurate determination of the difference spectrum obtained by the 

 addition of CO to a deoxygenated heart-muscle preparation (Fig. 1). The 

 peak in the difference spectrum was at 422 m/^, which showed that the pigment 

 was myoglobin and not haemoglobin, the CO compound of which absorbs 

 at 419-5 mfi in the difference spectrum. This conclusion was confirmed by 

 adding myoglobin and haemoglobin. The addition of the first pigment did 

 not cause any shift in the position of the band, but this moved towards a 



