Melibiose rates

The rate of oxidation of ethylene glycol was found268-269 to attain a broad maximum between pH 2.5 and 6. In a very complete study of the effect of pH on the periodate oxidation of carbohydrates, Neumiiller and Vasseur260 showed that the oxidation of maltose, melibiose, methyl a-D-... 

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... 

Rate of Hydrolysis of Phenyl a-D-Galactopyranoside and of Melibiose, by Different... 

Source of enzyme Ratio of rate of hydrolysis of melibiose to that of phenyl a-D-galactopyranoside... 

The curves shown indicate that ONPTG, maltose, and melibiose, in the range of the concentrations used, inhibit the O-nitrophenyl galactoside hydrolysis rate. We can see from the curves that a plateau is not reached at the high concentrations of inhibitors, meaning that the maximum velocity Vm is not reached. Thus, in order to determine Vm and Km, reciprocal plots should be drawn (Figure 17.6). 

That a-galactosidases are different from /3-galactosidases is shown by the difference in their behavior on precipitation with tannin (or alcohol), adsorption, and inactivation. " Among themselves, the various a-galactosidases are similar in the effect of pH, but they can be differentiated by virtue of their hydrolytic action on various substrates, for example, through the ratio of the rate of hydrolysis of melibiose to the rate of hydrolysis of phenyl /3-D-galactoside (see Table XIII, specificity). ... 

Fig. 3-25. Gradient elution of different sugar alcohols and saccharides. - Separator column Ion Pac AS6A eluent (A) water, (B) 0.05 mol/L NaOH + 0.0015 mol/L acetic acid gradient 7% B isocratically for 15 min, then to 100% B in 10 min flow rate 0.8 mL/min detection pulsed ampero-metry on a Au working electrode (post-column addition of NaOH) injection volume 50 pL solute concentrations 15 ppm inositol (1), 40 ppm sorbitol (2), 25 ppm fucose (3), deoxyribose (4), 20 ppm deoxyglucose (5), 25 ppm arabinose (6), rhamnose (7), galactose (8), glucose (9), xylose (10), mannose (11), fructose (12), melibiose (13), isomaltose (14), gentiobiose (15), cellobiose (16), 50 ppm turanose (17), and maltose (18).

Fig. 11.4.5. Separation of simple saccharides. Chromatographic conditions column, LiChrosorb Si 60 (5 jam) (250x4.0 mm) mobile phase, acetonitrile-water (75 25) containing 0.01% amine modifier flow rate, 3.0 ml/min detection, refractive index. Peaks Ri, ribose X, xylose F, fructose G, glucose S, sucrose Ma, maltose L, lactose Mb, melibiose Mt, maltotriose. Reproduced from Wight and Van Niekerk (1983b), with permission.

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