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The enzymic degradation of ovolecithin and certain other phosphoglycerides in ethereal solution by snake-venom phospholipase A is stimulated by Ca2+ ions. The optimum Ca2+ ion concentration varies between 40 and 80 /LM, when the lecithin concentration varies between 1*3 and 3-3 mM. 2. The phospholipase A activity of moccasin venom is inhibited by ethylenediaminetetraacetic acid and by Zn2+ and CU2+ ions, but not by iodoacetate or p-chloromercuribenzoate. 3. All the natural and synthetic L-c-lecithms studied lost one ester group/molecule of substrate in the presence of the enzyme. SynthetiC DL-Xlecithins lost only 0.5 mole of ester/molecule of substrate, whereas synthetic ,-lecithins did not undergo any enzymic hydrolysis. 4. Egg phosphatidylethanolamine was degraded by phospholipase A when the ethereal solution was adjusted to pH 7-0, and there is some evidence for the breakdown of phosphatidylserine and ethanolamine plasmalogen.

1. alpha-Mannosidase from jack-bean meal was purified 150-fold. beta-N-Acetyl-glucosaminidase and beta-galactosidase were removed from the preparation by treatment with pyridine. Zn(2+) was added during the purification to stabilize the alpha-mannosidase. 2. At pH values below neutrality, alpha-mannosidase undergoes reversible spontaneous inactivation at a rate dependent on the temperature, the degree of dilution and the extent of purification. The enzyme is also subject to irreversible inactivation, which is prevented by the addition of albumin. 3. Reversible inactivation of alpha-mannosidase is accelerated by EDTA and reversed or prevented by Zn(2+). Other cations, such as Co(2+), Cd(2+) and Cu(2+), accelerate inactivation; an excess of Zn(2+) again exerts a protective action, and so does EDTA in suitable concentration. 4. Neither Zn(2+) nor EDTA has any marked effect in the assay of untreated enzyme. In an EDTA-treated preparation, however, Zn(2+) reactivates the enzyme during assay. 5. It is postulated that alpha-mannosidase is a dissociable Zn(2+)-protein complex in which Zn(2+) is essential for enzyme activity.

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The visceral hump of the limpet, Patella vulgata, is a good source of several glycosidases (Conchie & Levvy, 1957). It has now been observed to contain an enzyme that hydrolyses p-nitrophenyl P-D-fucoside, and it was necessary to determine the relationship between this enzyme and the P-D-galac-'207 Vol. 87

1. alpha-d-Mannosidase from rat epididymis was purified 300-fold. beta-N-Acetyl-glucosaminidase and beta-galactosidase were removed from the preparation by treatment with pyridine. Zn(2+) was added during the purification to stabilize the alpha-mannosidase. 2. Mammalian alpha-mannosidase is most stable at pH6. At lower pH values it undergoes reversible spontaneous inactivation. The enzyme is also subject to irreversible inactivation, which is delayed by the addition of albumin. 3. Reversible inactivation of alpha-mannosidase is accelerated by EDTA and reversed or prevented by Zn(2+). Other cations, such as Co(2+), Cd(2+) and Cu(2+), accelerate inactivation and the action of a toxic cation can be prevented by Zn(2+) or by EDTA in suitable concentration. 4. The enzyme is stabilized by substrate and neither Zn(2+), EDTA nor a toxic cation has more than a small effect in the assay of an untreated preparation. The addition of Zn(2+) is necessary, however, for a constant rate of hydrolysis during prolonged incubation of the enzyme with substrate. In an EDTA-treated preparation, Zn(2+) reactivates the enzyme during the assay. 5. Evidence is presented that alpha-mannosidase is a dissociable Zn(2+)-protein complex, in which Zn(2+) is essential for enzyme activity.

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