Phytochrome Stability in Vitro

The decay in vitro of crude and purified phytochrome preparations, measured as decline in spectrophotometrically detectable photoreversibility, can be retarded by the addition of an as yet unidentified "protective factor" from the green tissue of peas. The factor has an apparent molecular weight of 465, is stable at elevated temperatures and to oxygen and high light intensity. It confers optimal protection at pH about 7.8 and is not greatly affected by treatment with hydrolytic enzymes. Protective factor also protects phytochrome against accelerated decay resulting from the addition of Cu(2+); it may therefore function as a metal chelator.