Particle-bound phytochrome: Spectral properties of bound and unbound fractions.

In-vitro irradiation of extracts of maize (Zea mays L.) coleoptiles with red light enhances phytochrome pelletability as was previously reported for Cucurbita pepo L. In neither case is this the result of an irradiation-induced increase in the level of total pelletable protein. The transformation difference spectra of bound and unbound phytochrome fractions obtained after both in-vivo and in-vitro irradiations are not significantly different. The data, therefore, do not indicate that irradiation-enhanced pelletability either in vivo or in vitro results from phytochrome denaturation. Other non-photoreversible changes in the molecule external to the chromophore environment might however still account for the observed pelletability.