... Thus, truncation of the C-terminaldomain and the binding of heme may affect the DNA-binding properties of the bHLH-PAS-A fragment.We further examined the binding of CO to the Fe(II)bHLH-PAS-A ... at421 nm and 543 nm at pH 8.0. The absorption max-ima of the Fe(II) species were at 426, 530 and 559 nm, and those of the Fe(II)–CO complex were at 422, 538 and 566 nm. On the other hand, optical ... absorptionspectra of the Fe(III), Fe(II) and Fe(II)–CO complexes of the PAS-A domain of NPAS2 were different fromthose of the bHLH-PAS-A domain (Fig. 1B and Table 1). Namely, in the Fe(III) form, the absorptionmaxima...