Molecular association of lectin and beta-glucosidase in corn coleoptile.

Corn coleoptile lectin is present with beta-glucosidase (EC. 3.2.1.2.1) in a single tightly bound molecular association complex (88.7 kDa). SDS-PAGE of the molecular complex dissociates into two main components. Of these, at a concentration of 75%, the corn coleoptile beta-glucosidase (60 kDa) is identified by enzymatic activity, with two 16-amino acid tryptic peptides displaying close homology with the primary structure of the enzyme. In separate experiments, we isolated homogenous monomeric enzyme of corn coleoptile. This allowed us to conclude that lectin properties like erythrocyte agglutination, found in the (88.7 kDa) molecular complex, is not due to the beta-glucosidase bound in it. Another protein (30 kDa) dissociated from the same SDS-PAGE gels rendered several tryptic peptides, including a 20-amino acid sequence V(L)GP(Q)W(A)GGSGGSPVDITAEPQR closely homologous to the putative beta-glucosidase aggregating factor (BGAF) precursor described recently. Tryptic peptide SAFTE(A)WN(V)ELK(V) was also present in the BGAF precursor. KFHEQR peptide was not present in BGAF precursor or any other protein sequence examined. Tryptic peptide TYGPFGA showed good homology with the BGAF precursor protein, FEGLYLFHTPLGSGAN peptide displayed identity with the BGAF precursor sequence. Thus, the 30 kDa protein does not appear to be identical to BGAF, but is rather a similar molecule which could be endowed with the lectin properties of the 88.7 kDa molecular complex.