Abstract
Membrane fractions from seedlings of four soybean [Glycine max (L.) Merr.] lines were examined by radioimmunoassay and hemagglutination assay for the 120,000 dalton soybean lectin. Two of the lines (Sooty and T-102) are genotypically lele and lack buffer-soluble soybean lectin; the remaining two lines (Beeson and Harosoy 63) are Le and produce seeds that contain the lectin (Su et al. 1980 Biochim. Biophys. Acta 629: 292-304). Both Triton X-100 (0.5% v/v) and nonidet P-40 (0.05% v/v) solubilized soybean lectin from membrane fractions of Le cotyledons. Triton X-100 interfered substantially with the assay of protein and hemagglutinating activity and was unacceptable for use in quantitative measurements. The nonidet P-40-solubilized soybean lectin from Le cotyledons was consistently present both in washed 13,000g and 82,500g membrane fractions, but it accounted for less than 1.5% of the total (buffer-soluble plus membrane-bound) soybean lectin. The membrane lectin was purified by the affinity chromatography procedure devised for soluble soybean lectin, and it was immunologically indistinguishable from authentic soybean lectin. Membrane fractions from Le cotyledons contained insignificant amounts of radioisotope-labeled soybean lectin that had been added during homogenization, and purified membrane fractions did not bind the lectin in the presence of the hapten, d-galactose. These controls make it unlikely that the membrane soybean lectin was of cytoplasmic origin. Soybean lectin and other hemagglutinins were not present in buffer-soluble or membrane fractions from lele cotyledons or from roots and hypocotyls of any of the lines.