Density Gradient Study of Victorin-Binding Proteins in Oat (Avena sativa) Cells

Victorin-binding proteins (VBPs) in oat (Avena sativa) cells were identified using native victorin and anti-victorin polyclonal antibodies. Homogenates of oat tissues were fractionated in continuous or discontinuous sucrose density gradients or with an aqueous two-phase method, and covalent binding sites of victorin were detected by western blotting. In a 20 to 45% (w/w) sucrose continuous density gradient, the 100-kD VBP was located in fractions of 37 to 44% sucrose, with a peak at 39% sucrose. Based on marker enzyme assays, plasma membranes peaked at 39 to 41% sucrose, mitochondria peaked at 41%, but Golgi and endoplasmic reticulum were in lower density fractions, peaking at 28 to 29% and 22 to 24% sucrose, respectively. The 100-kD VBP was not found in plasma membranes purified by the aqueous two-phase method or in mitochondria purified by discontinuous density gradient centrifugation. Victorin binding to 65- and 45-kD proteins was detected in all fractions in the continuous sucrose density gradients. The 65- and 45-kD proteins were both detected in purified plasma membranes, but only the 65-kD protein was detected in purified mitochondria. The subcellular location of VBPs was the same in sensitive and resistant oat cells.