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Abstract
The similar electrophoretic mobilities and sizes of several of the phycobiliproteins,
which are derived from the photosynthetic apparatus of cyanobacteria and eukaryotic
algae, render their separation and quantitation a challenging problem. However, we
have developed a suitable capillary electrophoresis (CE) method that employs a phytic
acid-boric acid buffer and laser-induced fluorescence (LIF) detection with a single
594 nm He-Ne laser. This method takes advantage of the remarkably high quantum yields
of these naturally fluorescent proteins, which can be attributed to their linear tetrapyrrole
chromophores covalently bound to cysteinyl residues. As such, limits of detection
of 1.18 x 10(-14), 5.26 x 10(-15), and 2.38 x 10(-15) mol/l were obtained for R-phycoerythrin,
C-phycocyanin, and allophycocyanin proteins, respectively, with a linear dynamic range
of eight orders of magnitude in each case. Unlike previously published CE-LIF methods,
this work describes the separation of all three major classes of phycobiliproteins
in under 5 min. Very good recoveries, ranging from 93.2 to 105.5%, were obtained for
a standard mixture of the phycobiliproteins, based on seven-point calibration curves
for both peak height and peak area. It is believed that this development will prove
useful for the determination of phycobiliprotein content in naturally occurring cyanobacteria
populations, thus providing a useful tool for understanding biological and chemical
oceanographic processes.