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Plant Physiology 65:6-12 (1980)
© 1980 American Society of Plant Biologists

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Articles

Light-induced Changes in Allophycocyanin 1

Itzhak Ohad2, Hans-Jörg A. W. Schneider3, Steven Gendel and Lawrence Bogorad

The Biological Laboratories, Harvard University, Cambridge, Massachusetts 02138

Several lines of evidence indicate that allophycocyanin is the previously unidentified "phycochrome" observed in extracts of blue-green algae.

Fractions containing phycoerythrin, phycocyanin, and allophycocyanin and exhibiting light-induced absorbance changes were prepared from extracts of Nostoc muscorum and Fremyella diplosiphon by isoelectric focusing. Illumination of such fractions with red light (650 nanometers) causes a reduction in absorbance at 620 nm (~=1 to 2%) and an increase at 560 nm. The effect, (previously observed by Björn and Björn [1976 Physiol Plant 36: 297-304]) is reversible, upon illumination with green light (550 nm). Selective immunoprecipitation of the phycobiliproteins indicates that allophycocyanin is the photoresponsive pigment.

At pH 4.0 to 4.2, allophycocyanin purified from the same algae or from Phormidium luridum exhibits a light-induced absorbance change at 620 nm, which coincides with its absorption maximum at this pH; the fluorescence emission of allophycocyanin under these conditions is at 647 nm and its S20,w is 2.28, compatible with an {alpha}1{beta}1 polypeptide composition. At neutral pH (5.8 to 7.0), allophycocyanin aggregates have a sedimentation coefficient of 4.8 (~={alpha}3{beta}3) and an additional absorption peak at 640 nm appears while that at 620 nm remains unaffected. The fluorescence emission maximum of the larger aggregate is at 667 nm and the light-induced change in its absorption is shifted to 650 nm. The effect of pH changes in the range 4.0 to 7.0 on the spectral and aggregation properties of allophycocyanin is completely reversible. Changes in pH which affect allophycocyanin aggregation have parallel effects on absorption and fluorescence maxima as well as on the light-induced absorbance changes of the biliprotein.

No evidence is provided to resolve whether this phycochrome plays the role of an adaptochrome.

2 Current address: Department of Biological Chemistry, The Hebrew University, Jerusalem, Israel.

3 Current address: Botanisches Institut der Universitat Köln, 5 Köln 41, Gyrhofstrasse 15, West Germany.

1 This research was supported in part by a grant from the National Science Foundation and in part by the Maria Moors Cabot Foundation of Harvard University.






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