Melibiase yeast

The extracellular enzymes of yeast are glycoproteins and include invertase and acid phosphatase. Strains of Saccharomyces carlsbergensis but not S, cerevisiae also possess melibiase. Yeast invertase has a minimum molecular weight of 27 000 contains 50 % mannan and 2-3 % glucosamine [43]. The precise location of the extracellular enzymes is still uncertain. They may occupy the space (periplasm) between the membrane and the bulk of the wall components, be anchored to the membrane via protein or covalently associated with other mannan or even glucan molecules. 

The a-D-galactopyranosidases are usually known as melibiases, in that melibiose is the most available substrate hydrolyzed specifically by a-D-galactopyranosidase. Melibiases have been encountered (see Table IV) in yeast,10 bacteria, molds, higher plants,36 and a few lower animals,37... 

A relatively more active source of melibiase is crude invertase from brewers yeast. Yeast melibiase is nearly free from /J-D-galactosidase, but it contains /3-D-mannosidase as well as /3-D-fructofuranosidase.23... 

When acted upon by invertase preparations containing melibiase (from brewers yeast), all the raffinose oligosaccharides, including planteose, are hydrolyzed to monosaccharides.23,42... 

Conditions necessary for the reversal of hydrolytic action have been applied by French to the synthesis of small amounts of galactobiose and galactotriose (isolated in crystalline form).33 The reactions catalyzed by yeast melibiase are as follows. 

Synthesis of manninotriose and a higher oligosaccharide,33 by trans-galactosylase action of yeast melibiase on melibiose, has already been noted in a preceding paragraph. 

Both samples were directly tested by paper chromatography and gave close agreement with the rotation methods. Emulsin preparations, as substitutes for yeast melibiase, have been found by the authors to have very low activities and defatted almond meal extracts showed a content of sucrose, glucose, and fructose on paper chromatograms. 

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