Cellobiose rates

Fig. 3.—A. Initial Slope Approximation to Determine the Initial, Nonselective, Spin-Lattice Relaxation Rate of H-S of 2,3 S,6-Di-0-isopropylidene-a-D-mannofuranose (2) in Me2SO-d Solution. (Points between 0.01 and l.SS s were selected for tracing the best straight line.) B. The Same as in A for H-1 of a Partially Deuterated Sample of 1,6-Anhydro- -cellobiose Hexaacetate (3). [Note that the relaxation of H-1 is strongly dependent on the choice of I value. An R (ns) value of 0.24s was obtained from the data points 0 t 5s, where a value of 0.18 s was obtained from the terminal decay 5 lOs (see text).]...

Freudenberg, Kuhn and their co-workers showed that both the velocity constants and the courses followed by the hydrolyses of these various polymers can be accounted for by postulating that one or the other or both of the terminal linkages, a and h of Table VIII, in these various species hydrolyze more rapidly than the internal c linkages. All of the latter can be assumed to hydrolyze at the same rate. If, for example, one of the two terminal linkages, a or 6, in an x-mer reacts at a rate equal to cellobiose, 1.07 X10, and the rate for each of the other X —2 linkages corresponds to the initial average rate, 0.305 X10, of hydrolysis of the bonds in cellulose then the calculated... 

Hydrolysis of delignified wheat straw up to 90% was obtained in 96 hours with the cellulase system produced in SSF with wheat straw. It took only 72 hours to obtain over 90% hydrolysis of wheat straw with cellulase system produced with SSF on Pro-cell (Table VII). It is interesting to note that the quantity of cellobiose in the hydrolysate obtained with the cellulase system produced on Pro-cell was higher than that of the cellulase system produced on wheat straw. This is consistent with the observation that cellulase system produced on Pro-cell had a lower ratio of FP cellulase )3-glucosidase (1 0.77) as compared to that produced on wheat straw (1 1.2). However, this cellulase system had a faster hydrolysis rate it took only 72 hours to obtain over 90% hydrolysis. This might be related to cotton hydrolyzing activity of this cellulase system (Table V). 

Kinetics of Bound and Free Enzyme. The kinetics of the IME were obtained with the recirculating differential reactor system as described above. The appropriate flow rate, the temperature optimum, and pH optimum as described above were used to most accurately establish the kinetic parameters for this IME emgmie. Substrate solutions from 3 to 150 mM cellobiose in 10 mM sodium acetate were appropriate for this portion of the study. Results were analyzed with the ENZFTT software package (Elsevier Publishers) that permits precise Lineweaver-Burk regressions. 

Figure 3. Relationship between concentrations of cellobiose, D-glucose, cAMP, glucose-l-phosphate and sopherose and rate of cellulase thesis according to Yagil and Yagil (52).

Proceeding on the same line, Hagerdal et al. reported that perfluorinated resin supported sulfonic sites (NATION 501) can hydrolyze disaccharides [25]. In particular, these authors studied the effect of the addition of sodium chloride in the hydrolysis of cellobiose, a subunit of cellulose much more resistant to hydrolysis than sucrose. They observed that the presence of sodium chloride in water dramatically increased the conversion of cellobiose. Indeed, in the presence of 10 wt% of sodium chloride, 80% of cellobiose was converted at 95°C after 6 h. For comparison, when 1% of sodium chloride was added, only 50% of cellobiose was hydrolyzed. It should be noted that without addition of sodium chloride only 15% conversion was achieved, thus pushing forward the key role of sodium chloride on the reaction rate. Effect of salt on the reaction rate was attributed to a change of the pH caused by the release of proton in the reaction medium (due to an exchange of the supported proton by sodium). 

As expected, mesoporous silica-supported sulfonic sites were able to catalyze the hydrolysis of cellobiose. Indeed, at 448 K, 90% of cellobiose was hydrolyzed within 30 min of reaction with an apparent activation energy ( = 130 kJ moF ) similar to that of reactions promoted by homogeneous organic acid catalysts [33]. The hydrolysis reaction rate is proportional to the concentration of hydrated... 

There are two reasons for the measurable cellobiose concentration in the T. viride cellulase hydrolyzed syrups. The most likely is that T. viride has rather poor / -glucosidase activity so that cellobiose accumulates. Evidence of this is that additions of / -glucosidase to the T. viride cellulase improves its activity. A second reason is that the / -glucosidase enzyme is strongly glucose inhibited. Hence the rate of cellobiose hydrolysis slows down as the glucose concentration rises, allowing cellobiose to accumulate. 

K — reaction rate constant Eads = grams of absorbed enzyme/gram of cellulose 12 — cellobiose inhibition concentration, g/L... 

In order to measure the enzyme activity and the initial rate of reaction, 5 mL of cellobiose (lOOmumol/mL) and 44 mL of buffer solution were placed in a stirred vessel. The reaction was initiated by adding 1 mL of enzyme (beta-glucosidase) solution which contained 0.1 mg of protein per mL. At 1,5,10,15, and 30 minutes, O.lmL of sample was removed from the reaction mixture and its glucose content was measured. The results were as follows ... 

In ammoniacal solutions of copper salts, the oxidation products are likely to contain nitrogen thus, hexoses give oxalic acid, imidazoles, hydrogen cyanide, and urea. Kinetic studies have been reported for the reaction of Cu(II) in the presence of ammonia with maltose, lactose, melibiose, and cellobiose.190 For the oxidation by tetraamminecopper(II) in ammoniacal and buffered media the rate of reaction is first order in disaccharide concentration, order one-half in ammonia concentration, but it is independent of Cu(II) concentration. The reaction rate is decreased by the addition of ammonium chloride, because of the common ion effect. These kinetics suggested mechanisms involving an intermediate enediolate ion, with the rate of reaction being equal to the rate of enolization.191 A similar mechanism has been proposed for the oxidation of D-fructose by a copper-pyridine complex in an excess of pyridine.192... 

Physical or chemical modification of a substrate may additionally selectively affect transformation or uptake Keil and Kirchman (1992) compared the degradation of Rubisco uniformly labeled with 3H amino acids produced via in vitro translation to Rubisco that was reductively methylated with 3H-methane. Although both Rubisco preparations were hydrolyzed to lower molecular weights at approximately the same rate, little of the methylated protein was assimilated or respired. The presence of one substrate may also inhibit uptake of another, as has been demonstrated for anaerobic rumen bacteria. Transport and metabolism of the monosaccharides xylose and arabinose were strongly reduced in Ruminococcus albus in the presence of cellobiose (a disaccharide of glucose), likely because of repression of pentose utilization in the presence of the disaccharide. Glucose, in contrast, competitively inhibited xylose transport and showed noncompetitive inhibition of arabinose transport, likely because of inactivation of arabinose permease (Thurston et al., 1994). 

---