Galactose oxidase. An enzyme with lectin properties

Utilization of enzyme-substrate interactions in analytical chemistry

Enzymes are capable of a highly specific interaction with a variety of substances including their respective substrates. This review summarizes how such interactions may be used in analytical (bio-)chemistry, e.g., for the elucidation of the binding mechanism, the determination of the binding strength, the carting of the binding site, or the screening of possible substrate/inhibitor molecules. Possible assay formats such as analytical affinity chromatography, affinity capillary electrophoresis (ACE), conventional affinity gel electrophoresis (AEP), and related techniques are discussed together with examples of recent applications. In addition a brief section on enzyme-substrate reactions as tools in analytical chemistry is included, since these are perhaps even more important to analytical (bio-)chemistry. The development and application of bioanalytical systems and especially biosensors in various fields including medicine, biotechnology, agriculture, defense and foodstuffs are considered.

Characteristic features of an alpha-galactosidase from mung beans

Two molecular forms, I and II (high and low molecular mass) of alpha-galactosidase were demonstrated in dry mung beans and a multi-step procedure was developed for isolating the tetrameric enzyme I in good yield. Two affinity chromatographic techniques were employed and an overall 10 000-fold purification was achieved. The enzyme was able to catalyse the hydrolysis of alpha-galactosidic linkages as well as agglutinate rabbit erythrocytes (clot formation). The clot was temporary and dissolved on longer incubation, yielding free galactose. The pH optima for both activities were similar. The enzyme also destroyed human-blood-group-B activity and increased H activity. The effect of pH on Km and Vmcx of the enzyme indicated the importance of carboxyl (pK approximately equal to 4.0) and histidine (pK approximately equal to 6.5) groups for activity. This was confirmed by amino acid modification experiments in the absence and presence of the substrate. The stoichiometry of enzyme inactivation showed the probable presence of 12 carboxyl groups and 9 histidine imidazole groups/molecule enzyme in the active site. The effects of modification of the groups on enzymic and hemagglutinating activities were parallel. A model explaining the display of both the activities by the enzyme, is presented in which hemagglutination is shown to be due to the formation of slightly stable enzyme-substrate complex. It is proposed that a true lectin should not alter the covalent status of the binding sugar.

Determination of the interaction of lactate dehydrogenase with high-molecular-weight derivatives of AMP by affinity electrophoresis

The interaction of lactate dehydrogenase with high-molecular-weight derivatives of AMP was studied by affinity electrophoresis in an alkaline buffer system and by means of kinetic measurements. AMP was coupled to synthetic hydroxypropylmethacrylamide copolymers through glycine, 6-aminohexanoic and 12-aminododecanoic spacer arms. The values of the dissociation constants (K) of the lactate dehydrogenase isoenzymes--immobilized AMP complexes determined by affinity electrophoresis decreased with increasing length of the spacer arm. Lactate dehydrogenase was competitively inhibited by high-molecular-weight derivatives of AMP; values of the inhibition constants (Ki) also depended on the spacer arm: the longer the spacer arm the stronger was the interaction between the enzyme and the inhibitor. Ki values for high-molecular weight derivatives of AMP were lower than those obtained for free AMP.

Ultrastructural localization of soybean agglutinin on thin sections of Glycine max (soybean) var. Altona by the gold method

Soybean agglutinin (SBA) has been localized in Glycine max (soybean) var. Altona at the ultrastructural level by the gold method. SBA was detected by marking thin sections of different part of the seed with gold granules (12 nm in size) labelled with anti-SBA antiserum. Upon examination by transmission electron microscopy, the lectin was found uniformly distributed in most of the protein bodies of the cotyledon. SBA was also present in the embryo axis.