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B Nidetzky

Publications and source records attributed to B Nidetzky.

41 records · Page 3Linked to original sources
PubMed1997

alpha-1,4-D-glucan phosphorylase of gram-positive Corynebacterium callunae: isolation, biochemical properties and molecular shape of the enzyme from solution X-ray scattering.

The alpha-1,4-D-glucan phosphorylase from gram-positive Corynebacterium callunae has been isolated and characterized. The enzyme is inducible approx. 2-fold by maltose, but remarkably not repressed by D-glucose. The phosphorylase is a homodimer with a stoichiometric content of the cofactor pyridoxal 5'-phosphate per 88-kDa protein subunit. The specificity constants (kcat/Km, glucan) in the directions of glucan synthesis and degradation are used for the classification of the enzyme as the first bacterial starch phosphorylase. A preference for large over small substrates is determined by variations in the apparent binding constants rather than catalytic-centre activities. The contribution of substrate chain length to binding energy is explained assuming two glucan binding sites in C. callunae phosphorylase: an oligosaccharide binding site composed of five subsites and a high-affinity polysaccharide site separated from the active site. A structural model of the molecular shape of the phosphorylase was obtained from small-angle solution X-ray scattering measurements. A flat, slightly elongated, ellipsoidal model with the three axes related to each other as 1:(0.87-0.95):0.43 showed scattering equivalence with the enzyme molecule. The model of C. callunae phosphorylase differs from the structurally well-characterized rabbit-muscle phosphorylase in size and axial dimensions.

Animals↗
PubMed1997

Induction of aldose reductase and xylitol dehydrogenase activities in Candida tenuis CBS 4435.

In this study the ability of various sugars and sugar alcohols to induce aldose reductase (xylose reductase) and xylitol dehydrogenase (xylulose reductase) activities in the yeast Candida tenuis was investigated. Both enzyme activities were induced when the organism was grown on D-xylose or L-arabinose as well as on the structurally related sugars D-arabinose or D-lyxose. Mixtures of D-xylose with the more rapidly metabolizable sugar D-glucose resulted in a decrease in the levels of both enzymes formed. These results show that the utilization of D-xylose by C. tenuis is regulated by induction and catabolite repression. Furthermore, the different patterns of induction on distinct sugars suggest that the synthesis of both enzymes is not under coordinate control.

Aldehyde Reductase↗
PubMed1994

Cellulose hydrolysis by the cellulases from Trichoderma reesei: adsorptions of two cellobiohydrolases, two endocellulases and their core proteins on filter paper and their relation to hydrolysis.

Separate binding of several purified cellulolytic components of Trichoderma reesei on to filter paper was studied and concomitant hydrolysis rates evaluated. Enhancement of mass transfer from the bulk liquid to the solid substrate by agitation has two different effects on adsorption depending on the type of enzyme: (i) the fraction of cellobiohydrolase II (CBH II) and endoglucanase III (EG III) bound at equilibrium is increased, whereas (ii) the rate but not the extent of cellobiohydrolase I (CBH I) and endoglucanase I (EG I) adsorption is affected. The adsorption of CBH I core, a component lacking the cellulose-binding domain (CBD), is, however, not significantly influenced by mass transfer. The CBH I interdomain peptide (present in CBH I core b) does not participate in adsorption but enhances stability. The adsorption of CBH I core proteins is a fully reversible process whereas that of the intact CBH I is not. Thus, the interaction of the CBD with filter paper apparently accounts for the mass-transfer-limited binding rate and also for the irreversible adsorption of intact CBH I. Adsorption isotherms at 50 degrees C indicate very similar relative association constants for the intact cellulases (0.24-0.30 l/g of cellulose), but drastically reduced values for CBH I core proteins (0.03 l/g of cellulose). The specific activities of adsorbed CBH I and of its core proteins are identical and a linear relationship between adsorption and rates of hydrolysis is found only for these enzymes. Thus, non-productive binding on to cellulose seems evident in the case of CBH II and EG III but not CBH I.

Adsorption↗
PubMed1994

Cellulose hydrolysis by the cellulases from Trichoderma reesei: a new model for synergistic interaction.

The hydrolysis of Whatman no. 1 filter paper by purified cellulolytic components from Trichoderma reesei and the synergistic action of binary combinations of these enzymes on the same substrate were investigated. At 20 milligrams filter paper, enzyme concentrations needed to obtain half-maximal hydrolysis rates (KE values) were in the 3-4 microM range for the cellobiohydrolases (CBHs) and 0.05-0.10 microM for the endoglucanases (EGs). Catalytic-core proteins of CBH I and EG III, lacking the cellulose-binding domain, exhibit KE values 2.3 and 5.1 times higher than those of the intact enzymes. In synergistic combinations of two cellulases, the KE value of at least one enzyme was 3-10-fold reduced. CBH I/CBH II and CBH I/EG III combinations showed the most powerful synergism, and optimal ratios were a function of the total protein concentration. Results obtained in activity and adsorption assays using filter paper pretreated with one component, followed by inactivation and subsequent hydrolysis with the same or another cellulase component, point to a sequential enzymic attack of the cellulose and seems consistent with the mathematical model presented.

Adsorption↗