Fractionation of particulate material from maize coleoptile homogenates with polyethylene glycol

Polyethyleneglycol (PEG) has been used to sediment particulate material from maize coleoptile homogenates at low centrifugal forces. The resuspended sediments were used for N-1-naphthylphthalamic acid (NPA)-binding studies. Binding activity was influenced by monovalent cations in the resuspension medium, but even at concentrations of up to 1.2 M NaCl or 0.5 M LiCl or CsCl, half of the binding activity was still recovered. Binding activity was influenced by divalent cations, because it decreased when Ca(2+) and Mg(2+) ions in the medium were complexed with EDTA. Fractionated sedimentation using increasing concentrations of PEG resulted in two peaks of NPA-binding activity at about 3% and 6% PEG. The 3% peak cintained enzymatic markers for mitochondria and endoplasmatic reticulum while the 6% peak contained NPA-binding activity only. Possible explanations for the bimodal distribution of NPA binding after fractionated PEG precipitation are discussed.