Melibiose, hydrolysis

The naturally-occurring 1,6-linked glucose polymers furnish other sources of 2,3,4-trimethyl-D-glucose, which has been isolated from the hydrolysis products of the methyl ethers of gentiobiose,112 118 melibiose,114 raffmose106 116 and dextran.78 74,116... 

This enzyme [EC 3.2.1.22] catalyzes the hydrolysis of melibiose to yield galactose and glucose. It will also act on terminal, nonreducing a-D-galactose residues in a-D-galactosides. In addition, it will hydrolyze a-D-fucosides. 

Melibiose [0-a-D-galactopyranosyl-(l—>6)-D-glucopyranose] is a constituent of the trisaccharide raffinose (see Section II,2,f), and is liberated on hydrolysis of the latter by invertase. A detailed, structural elucidation of this disaccharide was described by French.115 Melibiose is found in the exudates115 and nectaries204 of several plants, and is also found in the tissues of various plants.75,110,123 205-209 In Aconitum... 

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... 

A comparative study of the action of yeast invertase on sucrose, raffinose, and stachyose was reported by Adams, Richtmyer and Hudson (see Table V).23 Hydrolysis by invertase has been found to give D-fruc-tose, in each case, and the complementary aldose D-glucose, melibiose, or manninotriose. In general, the same products are formed as in mild acid hydrolysis. 

In 1951, Whistler and Durso reported68 the isolation of epimelibiose by partial, acid hydrolysis of the polysaccharide guaran, followed by charcoal-column fractionation of the products. ThA material was obtained in anhydrous crystalline form from a mixture of methyl and butyl alcohols it had m.p. 201°, [a]26D + 120.9° — +124.6° in 36 hr. (c 2, in water). The yield was 2.2% of the weight of guaran used. Epimelibiose has also been produced72" in crystalline form following the ammonia-catalyzed alkaline isomerization of melibiose. 

The exact structure of raffinose follows most simply from the fact that it is cleaved by mild acid hydrolysis, or by invertase action, to give D-fructose and melibiose,7 and by almond-emulsin a-D-galactopyrano-sidase to give D-galactose and sucrose.16... 

De Whalley and his coworkers have made extensive studies on the application of paper chromatography to raffinose. To separate raffinose from large proportions of sucrose, a 1-butanol-benzene-pyridine-water solvent was used.140 81 To avoid pyridine, a 1-propanol-ethyl acetate-water mixture was recommended.141 As a color reagent, a-naph-thol-phosphoric acid was used. In this manner, less than 1 % of raffinose in cane sugar could be separated and determined. Partial hydrolysis of the raffinose, using invertase directly on the filter paper, proved useful in some instances.93 142 Melibiose was then detected with 3,5-dinitrosali-cylate142 or with diethyl-p-phenylenediamine sulfite.93... 

O-Nitrophenyl glactoside hydrolysis with /3-galactosidase in the absence and presence of three inhibitors, O-nitrophenyl /S-D-thiogalactoside (ONPTG), maltose, and melibiose, was studied at 25°C in pH 7.5 buffer. Table 17.1 shows the optical densities at 410 nm of the PNP formed, expressed per minute. 

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). 

Figure 17.5 Velocity of hydrolysis of O-nitrophenyl galactoside with /J-galactosidase in the absence (a) and presence of inhibitors, 3 x 10 4 MONPTG (b), 0.26 M maltose (c), and 0.17 M melibiose (d).

Melibiose (6-0-(3-D-Gal-D-G1c) (disaccharide) Widespread in plant exudates from Raffinose hydrolysis Sweet [[Pg.404]

Only one tri-saccharose is important. It is known as raffinose and has the composition Ci8H320]6. It is found in beets and is present in the molasses after the sucrose sugar is crystallized out. It is also found in barley and in cotton seeds. When this tri-saccharose hydrolyzes it yields first a di-saccharose known as melibiose and a monosaccharose fructose. The di-saccharose is then further hydrolyzed and yields two molecules of mono-saccharose, viz., glucose and galactose. The complete hydrolysis of the tri-saccharose, therefore, is as follows. 

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). ... 

Comparison of Hydrolysis of Melibiose and Phenyl a-T>-Oalactoside with a-Galoctosidoses from Various Sources ... 

Fletcher and Diehl, in studying the preparation of melibiose from raffinose by the fermentative hydrolysis of the trisaccharide, noticed a new form of the disaccharide. By observing the mutarotation of the new form, and by comparing the infrared spectra with that of an authentic... 

Moelwyn-Hughes EA (1929) The kinetics of the hydrolysis of certain glucosides, part III. p-methylglucoside, cellobiose, melibiose, and turanose. Trans Faraday Soc 25 503-520... 

Hydrolysis of melibiose with acid or with an a-galactosidase gives D-galactose and D-glucose. 

Methylation and hydrolysis of melibiose give 2,3,4,6-tetra-O-methyl-D-galactose and 23,4-tri-O-methyl-D-glucose. 

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