The interaction of riboflavin with a protein isolated from egg white has been studied spectrofluorimetrically at different pH values. In 0.1 M phosphate buffer pH 7.0; 1:1 complex formation occurs with the association constant Ka = 7.7-10(7) M-1. In the presence of 0.033% sodium dodecyl sulphate, the complex dissociated with a rate constant of 4-10(-2) sec-1 at 29 degrees C. The binding was sensitive to pH and to the antibodies produced against the protein. On lowering the pH from 7 to 4 the binding affinity decreased approximately 100-fold and below pH 4, the binding could not be detected at all. These data, together with those obtained by measuring the fluorescence intensities of riboflavin in presence of N-bromosuccinimide oxidized- and disulphide reduced apoprotein, suggest that carboxyl functions, 1-2 tryptophan residues and 2-3 disulphide bridges are essential for binding. The emission spectra of the protein under different conditions upon excitation at 280 and 295 nm were analyzed to calculate the quantum yield (Q) and the efficiency of energy transfer (e) from tyrosine to tryptophan residues. From these data it was concluded that the energy transfer did not occur with equal efficiency under all conditions and that the tryptophan residues responsible for the riboflavin binding are more accessible to N-bromosuccinimide oxidation than others.

Binding Sites↗

PubMed1975

Interaction between lectin from Ricinus communis and liposomes containing gangliosides.

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Agglutination↗

PubMed1975

Studies on the interaction of concanavalin A with glycoproteins.

Lectins (phytohaemagglutinin) are known to have the unique property of binding with certain specific sugars, polysaccharides and glycoproteins. Although the kinetics of interaction between lectins and sugar have been extensively studied, the binding characteristics of the lectins with various glycoproteins are not well understood. In this laboratory a systematic study has been initiated in relation to the interaction of lectins with glycoproteins. Concanavalin A is known to bind alpha-glucosides, mannosides and biopolymers having these sugar configurations. A galactose binding protein from caster bean has been purified to homogeneity and was found to contain mannose. This lectin was used as the source of glycoprotein for studying its interaction with concanavalin A. This study showed that the interaction is temperature dependent and the dissociation is time and alpha-methyl glucoside concentration dependent. This has led to speculate a model for cell-lectin interaction. Using concanavalin A it has been shown that all the lysosomal enzymes from brain studied were glycoprotein in nature. Moreover, using Sepharose-bound concanavalin A it has been possible to devise a method by which these lysosomal enzymes could be purified considerably. With the knowledge that the interaction between lectin and glycoprotein is not only dependent on the specific sugar present in the glycoprotein, but also on the nature of the glycoprotein it was possible to develop a novel method for immobilizing various glycoprotein enzymes, such as arylsulphatase A, hyaluronidase and glucose oxidase.

Animals↗

PubMed1975