Enzyme carbohydrate stabilization

In this article the preparation of one class of carbohydrate-enzyme conjugates, prepared by attachment of dextran to enzymes, is described in some detail and the properties of enzymes modified in this way are discussed. The molecular basis of enzyme stabilization by coupling with dextran is also considered. 

Magnesium aids in energy metabolism, promotes proper nerve function, and is involved with muscle activity. It also activates certain enzymes, stabilizes cell structures, and is used for the body to make cell protein, fats, and carbohydrates. Frequently, magnesium supplements are recommended for muscle cramping and other ailments, but our main interest right now is in how this electrolyte can affect blood pressure. 

The polar nature of ILs increases the solubility of polar substrates, such as carbohydrates, which ensures enhanced reaction rates. Other potential advantages are increased enzyme stability [107] or stereoselectivity [108]. Furthermore, the properties of ILs can be easily tailored by simply choosing another combination of ions. On the down-side, ILs are considerably more expensive than organic solvents and are more viscous, which complicates their handling. Preliminary data indicate that some components of ILs are quite toxic and are not easily biodegradable [109]. 

S. Yamamoto, Effects of Carbohydrates on Enzyme Stabilization during Drying, Proceedings of the Tenth International Drying Symposium, IDS 96,30 July-2 August, Cracov, Poland, in Drying 96, C. StrumiHo and Z. Pakowski (Eds.), Vol. B, 1267-1274 (1996). 

The stability of a phenylesterase in soil was considered to be the result of a carbohydrate-enzyme complex, although in this instance, the existence of a carbohydrate-protein bond through N-acetylhexosamine-tyrosine is postulated. Hyaluronidase treatment increases the activity of the enzyme. 

The laccase molecule is a dimeric or tetrameric glycoprotein, which contains four copper atoms per monomer, distributed in three redox sites. More than 100 types of laccase have been characterized. These enzymes are glycoproteins with molecular weights of 50-130 kDa. Approximately 45% of the molecular weight of this enzyme in plants are carbohydrate portions, whereas fungal laccases contain less of a carbohydrate portion (10-30%). Some studies have suggested that the carbohydrate portion of the molecule ensures the conformational stability of the globule and protects it from proteolysis and inactivation by radicals (Morozova and others 2007). 

No differences were found between the native and deglycosylated enzymes for the characteristics of pH range of stability, optimum pH, and adsorption to cellulose and milled wood. It can be concluded that the most important role of the carbohydrate chains in laccase III is the resistance to proteolysis in wood decay (15),... 

Although rat-epididymal a-D-mannosidase is not so convenient as the jack-bean enzyme for use as a carbohydrate reagent, it may be of particular interest in mammalian physiology. It differs from the plant enzyme in that the protein-Zn2+ complex is more readily dissociable, there being no pH at which the purified epididymal enzyme is completely stable (see Table VII). Greatest stability was displayed between pH 5 and 6, but inactivation was still marked unless Zn2+... 

Using gel filtration on columns of Sephadex G-200, Gascon and Ot-tolenghi142 discovered in Saccharomyces cerevisiae a form of /3-D-fruc-tofuranosidase of low molecular weight, and predicted correctly that this form would be found to be free from carbohydrate. This enzyme occurred within the protoplast its molecular weight (135,000) and specific activity were similar to those of the protein moiety of the external enzyme. The two /3-D-fructofuranosidases gave the same Km for sucrose, the same Km for raffinose, and the same pH optimum (3.5 to 5.5) for enzymic activity but their pH-stability curves differed, the internal enzyme being reversibly inactivated under acidic conditions, that is, below pH 5. 

The choice of a suitable immobilization method for a given enzyme and application is based on a number of considerations including previous experience, new experiments, enzyme cost and productivity, process demands, chemical and physical stability of the support, approval and safety issues regarding support, and chemicals used. Enzyme characteristics that gready influence the approach include intra- or extracellular location size surface properties, eg, charge/pi, lysine content, polarity, and carbohydrate and active site, eg, amino acids or cofactors. The size, charge, and polarity of the substrate should also be considered. 

Enzymes are protein catalysts of remarkable efficiency and specificity. Lipid, carbohydrate, nucleotide, or metal-containing prosthetic groups may be attached to these enzymes and serve as essential components of their catalyses by enhancing specificity and/or stability (8—13). Each enzyme has a specific temperature and pH range where it functions to its optimal capacity the optima for these proteins usually He between 37—47°C, and pH optima range from acidic, ie, 1.0 in the case of gastric pepsin, to alkaline, ie, 10.5 in the case of alkaline phosphatase. However, enzymes from extremely thermotolerant bacteria have become available these can function at or near the boiling point of water, and therapeutic use of these ultrastable proteins can be anticipated. 

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