Phosphomannanase (PR-Factor), an Enzyme Required for the Formation of Yeast Protoplasts

The PR-factor, an enzyme necessary for the production of protoplasts from yeast, was identified and was named phosphomannanase. The enzyme released mannan and mannan-proteins from yeasts harvested in the logarithmic phase of growth. The size of the molecules released was greater than 200,000 daltons, which indicated that the enzyme splits very few bonds of the yeast wall. The PR-factor also depolymerized phosphomannans produced by theHansenula species. The degradation of these substances was due to the splitting of mannosidic bonds. However, the phosphodiester bonds present in these phosphomannans were involved in the specificity of the enzyme, and the number of mannosidic bonds cleaved was dependent on the number of phosphodiester bonds present. We studied the products of degradation ofHansenula phosphomannans and were unable to identify the exact bond split by the enzyme. After enzymatic digestion and subsequent splitting of phosphodiester bonds, phosphomannan Y-2448 yielded products too complex to be separated. Phosphomannan Y-1842 was shown to have a structure more complex than that previously proposed. The action of the enzyme on the phosphate-rich walls ofSaccharomyces was studied. Mannan, containing intact phosphodiester bonds, was released from the walls. Mild acid hydrolysis of this released material split the diester bonds to yield monosaccharide and polysaccharide terminated in mannose-6-phosphate. From these products, we deduced that the enzyme cleaved a mannosidic bond adjacent to a mannose, which is also phosphodiester linked through carbon 1. The significance of phosphodiester bonds in the attachment of mannan and mannan-protein enzymes to the wall of yeast is discussed.