A Photoreversible 39 Kdalton Fragment from the Pfr form of 124 Kdaltonoat Phytochrome

Abstract

Limited proteolysis of 124 kdalton oat phytochrome in the Pfr form is described which leads to a photoreversible 39 kdalton fragment. Whereas the absorption maximum of the Pr form is only slightly shifted (from 667 to 660 nm) no long-wavelength band is observed in the Pfr form. A “bleached” (i.e. low absorbing) form appears instead with a broad absorption maximum at 640 nm. This property corresponds with that of a 40.3 kdalton fragment obtained from pea phytochrome by limited proteolysis (Yamamoto and Furuya, Plant and Cell Physiol. 24, 713, 1983). Dark reversion of the bleached form to the Pr form is faster (t1/2 — 101 min) than dark reversion of 118 kdalton or 60 kdalton Pfr. Low temperature spectroscopy of the 39 kdalton fragment showed that the intermediates lumi-R and meta-Ra are formed like in intact phytochrome or 60 kdalton or 114/118 kdalton fragments. It is discussed that limited proteolysis removed that part of the peptide chain which is responsible for the interaction with the Pfr chromophore but that the site for interaction with the chromophore of Pr and the intermediates lumi-R and meta-Ra is still intact. © 1985, Walter de Gruyter. All rights reserved.