Hill activity in cell-free preparations of a blue-green alga

Abstract

The Hill-reaction activity of pigment-containing particles prepared from the blue-green alga, Anabaena variabilis, has been studied. Depending on the medium used for cell breakage and particle isolation, particles are obtained which have either largely lost or partially retained the accessory photosynthetic pigment, pycocyanin. Both types of particles show Hill-reaction activity to a variety to electron acceptors at rates which compare favorably to those seen with higher-plant chloroplasts. Only at limiting light intensities does the presence of phycocyanin in the particle appear to make a difference in the rate of the Hill reaction. The Hill-reaction activity of these preparations is unique in showing a marked stimulation by Mg²⁺.