Effects of organic and inorganic phosphate ions on the charge-transfer band of ferric myoglobin.

(1) Splitting of the charge-transfer band positioned at 630 nm of metmyoglobin disappeared on lowering the pH from 7.5 to 4.5 in the presence of Pi and PPi at the temperature of liquid N2. (2) The observed apparent pK value of the disappearance of the splitting depended upon the species of phosphate ions. (3) In the case of Pi, the low-temperature absorption spectra suggested that at least two phosphate ions bound to one myoglobin molecule.