PHOTOTRANSFORMATION OF PEA PHYTOCHROME-A INDUCES AN INCREASE IN ALPHA-HELICAL FOLDING OF THE APOPROTEIN - COMPARISON WITH A MONOCOT PHYTOCHROME-A AND CD ANALYSIS BY DIFFERENT METHODS

The photoreversible conformational change associated with the P-r --> P-fr transformation of a dicot phytochrome A (Pisum sativum, pea) has been probed by circular dichroism (CD) studies. Three different CD analysis methods have been used to determine the secondary structure of pea phytochrome A in both P-r and P-fr forms. We have shown that the secondary structure of dicot pea phytochrome A is very similar to the structure of monocot oat phytochrome A which was determined earlier [Sommer & Song (1990) Biochemistry 29, 1943-1948]. As with oat phytochrome A, an increase in the alpha-helical folding of the apoprotein takes place when photochrome in the P-r form is phototransformed to the P-fr form. This conformational change might well be a general characteristic of all phytochrome A's.