any one of the blue pigments of the group of phycobilins, phycocyanin proper or allophycocyanin, contained in blue-green and red algae. The molecular weight of phycocyanins varies from 134,000 to 273,000. The protein portion consists of globular proteins in associations of several subunits, each of which is covalently bonded to two to four chromophoric groups; these groups, known as phycocyanobilins, are chemically and spectrally identical for phycocyanin and allophycocyanin. Differences in the quaternary structures of these proteins account for the nonidentical position of the bands of absorption and fluorescence in the visible portion of the spectrum: maximum absorption is 615–622 nanometers (nm) for phycocyanins and 605–654 nm for allophycocyanins, and maximum fluorescence is 647–657 nm for phycocyanins and 663–670 nm for allophycocyanins. Because of its spectral properties, allophycocyanin is capable of transmitting light absorbed by phycoerythrins and phycocyanins to chlorophyll.