Isolectins of Phaseolus vulgaris. Physicochemical studies.

By a combination of solubility fractionation, continuous free-flow high voltage electrophoresis, molecular sieve and affinity chromatography on fetuin-Sepharose 4B, several lectin fractions of different isoelectric point were obtained from the seeds of Phaseolus vulgaris cv. "Processor". The albumin isolectin range comprised of five major lectin components with isoelectric points between pH 4.6 and 5.2, while the partly overlapping globulin isolectins contained several more lectin components with higher isoelectric points. The two groups had similar amino acid and sugar composition but were only partially identical by immunochemical criteria. The isolectins were also shown to be similar by physicochemical measurements with a common protomer weight value of about 119000. Values of so20,w, 6.84 and 6.76 S, and of V av, 0.712 and 715 ml/g, for the albumin and the globulin lectins, respectively, also indicated a close similarity. Both groups contained, in a slow equilibrium with the protomer, just over 10% of dimer and oligomers. In addition, the albumin lectins also contained a small, 2 S, dissociation product in a slow equilibrium with the protomer. The hydrodynamic data obtained for the albumin isolectins: [eta] = 0.063 dl/g; beta = 2.42 . 10(6) and f/fo = 1.56 indicated a highly voluminous particle with an effective volume of 8.6 . 10(-18) ml. This type of molecular arrangement was general for the major P. vulgaris seed glycoproteins and was, thus, suggested to be of potential importance for their physiological functioning during seed maturation and germination.