Spectral Properties of Chromophore-Containing Fragments Prepared from Pea Phytochrome by Limited Proteolysis1

Abstract

Five chromophore-containing fragments were prepared from pea phytochrome in PR form (monomer mol wt 114,000) by limited proteolysis with trypsin, thermolysin or chymotrypsin, and their absorption and circular dichroism (CD) spectra were determined. The fragments of mol wt 62,100 and 56,400 showed photoreversible transformation between P_R and P_FR like phytochrome. The smaller fragments of mol wt 40,300, 39,000 and 33,000 showed an absorption maximum at 657–660 nm (P₆₆₀) which was transformed to a bleached form (P_BL) after a brief red-light exposure. The phototransformation between P₆₆₀ and P_BL was repeatedly reversible. Both P₆₆₀ and P_BL showed a negative CD band in red region like P_R, in contrast with P_FR which has a positive band in far-red region. The nature of a chromophore domain of phytochrome and spectral properties of P_BL are discussed.