The effect of pH on both spectral types of R-phycoerythrin

There are two spectral types of R-phycoerythrin (RPE) in red algae. One is the triple peak type RPE with absorption maxima at 498,540 and 565 nm. The other is the double peak type RPE with absorption maxima at 498 and 565 nm, and an absorption shoulder at 540 nm. The former is present only in higher classes of the more advanced Florideophyceae, the latter occurs chiefly in the more primitive Bangiophyceae. When these two types of RPE are treated with buffer solutions with a broad pH range from 2.0 to 11.0, their absorption and fluorescence spectra remain unchanged within the range adjacent to neutral pH. At pH values higher than 9.6, the absorption and fluorescence spectra of triple peak type RPE still remain stable, but the absorption spectra of double peak type RPE produce gradually a protrusion similar to an absorption peak at about 540 nm. This phennomenon shows that there are certain differences in structure between these two types of RPE. Both types of RPE are naturally occurring products showing systematic developmental meaning in red algae. Contribution No. 1333 from the Institute of Oceanology, Academic Sinica.