Enzymes are present in higher plant tissues that rapidly degrade glycosylglycerides. The initial attack is by an acyl hydrolase (Section 7.2.5), which removes acyl groups from both positions and has very high activity in some tissues such as runner bean leaves or potato tubers. Indeed, homogeniza-tion of the latter at a suitable pH in aqueous media results in the complete breakdown of all membrane lipids within a minute! The activity of acyl hydro-lases (and other lipid degradative enzymes) in many vegetables even at low temperatures makes it necessary to blanch (boil) such products before storage in a deep-freeze.
Several acyl hydrolases, with slightly different specificities, have been purified from various plant tissues. The enzymes from runner bean leaves are remarkably stable to heating (only 10% activity is lost after 30 min at 70°C) and solvents and can be conveniently purified using hydrophobic chroma-tography. Further breakdown of the galactosylgly-cerides occurs by the action of a- and P-galactosidases.
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