MERCURIAL-INDUCED CIRCULAR DICHROISM CHANGES OF PHYCOERYTHRIN AND PHYCOCYANIN

1. 1. The effect of a mercurial on circular dichroism (CD) of B-phycoerythrin, R-phycoerythrin and C-phycocyanin has been investigated. 2. 2. B-phycoerythrin exhibits a double CD band centered at the longest wavelength absorption. Upon treatment with a mercurial, the double CD band appears to reverse its sign resulting in a different double CD band shifted toward shorter wavelengths. 3. 3. R-phycoerythrin, having three positive CD bands, lacks the double CD band both before and after mercurial treatment. 4. 4. C-phycocyanin from Anacystis nidulans shows two positive CD bands. The longer wavelength CD band at pH 5 is much greater than the shorter wavelength band. At pH 7, where both bands are of about the same intensity and are well separated, the longer wavelength CD band shifts to a shorter wavelength in the presence of a mercurial. 5. 5. Subsequent addition of mercaptoethanol brings about a partial regeneration of the longest wavelength positive CD band in the case of both R-phycoerythrin and C-phycocyanin but not with mercurial-treated B-phycoerythrin which produces a double CD band of opposite sign. 6. 6. These CD changes are discussed in connection with absorption spectral changes as well as with the dissociation and association aspects of these chromoproteins. © 1969.