Hydrolysis of galactomannans

According to Reese and Shibata,221 the biodegradative hydrolysis of galactomannan requires at least three different enzymes, namely, a-D-galactosidase, endo-/3-D-mannanase, and j3-D-mannosidase. In addition to these enzymes, there is also a report222 of a phosphorylase, identified as oligo-j8-D-mannosyl-(l— 4)-phosphorylase, which may take part in the degradation. These enzymes will now be discussed in detail. 

Endosperms, when isolated, accumulate galactose and mannose, but do not do so in intact seeds. This latter fact is illustrated in Figure 6.5 B, where the differences between the amounts of galactose and mannose released on hydrolysis of galactomannans (and the raffinose series oligosaccharides), and the accumulated levels of these monosaccharides in germinated carob seeds, can be seen clearly. 

Fig. 6.5. (A) Depletion of galactomannan in carob (x), lucerne ( ) and soybean (o). Redrawn from McCleary and Matheson, 1976 [99]. (B) Differences between the amounts of galactose and mannose released and accumulated during hydrolysis of galactomannan...

Ganter JL, Sabbi J, Reed WF. Real-time monitoring of enzymatic hydrolysis of galactomannans. Biopolymers 2001 59 226-242. 

Table I. Oligosaccharides produced on hydrolysis of carob galactomannan by p-mannanases...

This enzyme [EC 3.2.1.78], also known as mannan endo-l,4-j8-mannosidase and endo-l,4-mannanase, catalyzes the random hydrolysis of l,4-j8-D-mannosidic linkages in mannans, galactomannans, glucomannans, and galacto-glucomannans. 

The action of /3-D-mannosidase finally degrades the D-manno-oligo-saccharides, to afford free D-mannose molecules details of this process were given in an earlier article.12 An enzyme identified as oligo-/J-D-mannosyl-(l- 4)-phosphorylase719 may also take part in the mobilization of D-galactomannan in seeds. This enzyme, in the presence of orthophosphate, acts on D-manno-oligosaccharides (obtained from partial hydrolysis of D-mannan), and yields /3-D-mannosyl phosphate. 

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