The cryptic?-fructofuranosidase ofSaccharomyces rouxii

Abstract

The synthesis ofβ-fructofuranosidase in synchronously dividing cells ofS. rouxii was continuous (as opposed to periodic) throughout the budding cycle and followed the increase in cell mass. Similar patterns for cell mass and enzyme increases were observed even in phosphate-deprived cells which did not divide. Theβ-fructofuranosidase activity remained physically cryptic throughout the cell cycle as evidenced by analyses on equilibrium density gradient fractions. Theβ-fructofuranosidase activity released from mechanically disrupted cells resisted sedimentation when subjected to 131 000 g for 1 h, thus ruling out membrane association. Ethyl acetate was routinely employed to break the crypticity barrier. Enzyme in cell-free extract or in cells was equally sensitive to inactivation at pH values below 5 in the presence of ethyl acetate, which suggested that this is an inherent property of the enzyme in question and not a reflection of proteolytic inactivation. The status ofβ-fructofuranosidase in selected species of Saccharomyces was compared with that forS. rouxii and a close similarity withS. bisporus var.mellis was noted. The degree of crypticity encountered in genetically defined strains ofS. cerevisiae (e.g. ×2180 a/α) was relatively high (42%) compared with that for commercially derived bakers' and brewers' strains (about 6%). Extant data on the crypticβ-fructofuranosidase ofS. rouxii are evaluated and the utility of this system for studying enzyme translocation is discussed.