A kinetic method for the direct determination of cellobiose hydrolysis by β-glucosidases

TheSomogyi—Nelson colorimetric method is applied in a new manner which is more suitable for following the kinetics of cellobiose hydrolysis catalyzed by -glucosidase (EC 3.2.1.21). TheSomogyi—Nelson colour reagent, which is a mixture of the solutions of the reagent ofSomogyi and that ofNelson in a volume ratio of 1:1, is added to the enzyme-substrate solution at the very start of the reaction. The colour reagent reacts with the product (D-glucose). Under the reaction conditions (0.1M acetate buffer,pH = 5.0 and temperature 37°C) the colour reagent does not affect the enzyme activity. The method excludes any inhibition of the product, owing to the continuous removal of the latter by the colour reagent. The method suggested has been applied to monitor cellobiose hydrolysis with -glucosidase, contained in four cellulase enzyme preparations from various fungal sources. The values of theMichaelis parameters (Km, V) were determined.

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Eine kinetische Methode zur Verfolgung der Hydrolyse von Cellobiose durch ß-Glucosidasen

Zusammenfassung Die kolorimetrische Methode nachSomogyi undNelson wird nach einem neuen Verfahren zur Verfolgung der Kinetik der hydrolytischen Spaltung von Cellobiose, katalysiert durch -Glucosidase (EC 3.2.1.21), angewandt. Das Farbreagenz nachSomogyi undNelson (Mischung der Reagenzien vonSomogyi undNelson im Volumenverhältnis 1:1) wird der Enzym-Substrat-Lösung zu Beginn der Reaktion hinzugefügt. Das Farbreagenz tritt mit derD-Glukose in Reaktion, wobei unter den gegebenen Reaktionsbedingungen (0,1M Azetatpuffer,pH = 5,0 und 37°C) die Enzymaktivität nicht beeinflußt wird. Die entwickelte Methode wurde zur Verfolgung der Hydrolyse von Cellobiose durch ß-Glucosidasen, die in vier Enzympräparaten aus verschiedenen Pilzstämmen enthalten waren, angewandt. Es wurden dieMichaelis-Parameter (Km, V) bestimmt.

     

4-O-β-d-GLUCOPYRANOSYL-d-GLUCONIC ACID (CELLOBIONIC ACID) PRODUCED BY OZONATION OF CELLOBIOSE: ISOLATION BY HPLC AND ASSIGNMENT OF NMR CHEMICAL SHIFTS

Mild ozonation of cellobiose in acetic acid almost exclusively favors oxidation of the reducing end, thus yielding 4-O-β-d-glucopyranosyl-d-gluconic acid (“cellobionic acid”). This compound can be quantitatively separated from the substrate by preparative HPLC using acetonitrile/phosphate buffer on an aminopropyl silica column. The product was identified using one and two dimensional NMR techniques. ¹³C and ¹H NMR chemical shifts are reported.     

Direct electron transfer between heme-containing enzymes and electrodes as basis for third generation biosensors

Direct electron transfer (DET) between redox enzymes and electrodes found the basis for third generation biosensors. Recent investigations in the authors’ laboratories on the bioelectrochemistry of heme-containing proteins and enzymes, primarily peroxidases, but also cellobiose dehydrogenase, will be reviewed.