Studies on γ Globulin of Rice Embryo

Abstract

An improved method has been described for the isolation and purification of γ globulin from rice embryo. The method involves the extraction with phosphate buffer, pH 7.0 and ionic strength 0.1, the fractionation in saline solution of ionic strength 0.31, the removal of nucleic acids by precipitation with ammonium sulfate and the gel filtration chromatography on a Sephadex G-200 column. Although the preparations exhibited homogeneous patterns in sedimentation analysis, the electrophoretic patterns on polyacrylamide gels at pH 8.35 and ionic strength 0.11 exhibited at least two components. Three major components, γ₁, γ₂ and γ₃ globulins, were isolated by ion exchange chromatography on a DEAE Sephadex A-50 column. These components were revealed to be homogeneous in electrophoresis as well as sedimentation. N-Terminal amino acid compositions have also been described.

The molecular weight of γ₁ globulin was determined as 2.0 × 10⁵ by the Archibald method, and the intrinsic viscosity, [η], and the sedimentation coefficient, s_{20, w}^∘, were found to be 0.0424 dl/g and 7.26S respectively. These values indicated the large asymmetry of the protein. The protein was composed of 18 residues of hexose, 3 residues of pentose, 6 residues of hexosamine and 1751 residues of amino acids: Lys₅₈, His₄₇, Arg₁₄₈, Asp₁₂₆, Glu₂₇₃, Gly₁₆₁, Ala₁₄₄, Val₁₂₁, Leu₁₀₆, Ile₇₂, Pro₈₃, Ser₁₃₆, Thr₄₈, Hyp₆₈, Cys₁₇, Met₁₆, Tyr₄₄, Trp₈, Phe₇₅ and amide ammonia₁₆₃. The N-terminal amino acid analysis suggested that the protein was composed of ten subunits. The properties and the composition were discussed in comparison with those of the 7S globulin of soybean cotyledon.