Purification of the Internal Invertase of Yeast*

Most of the studies on yeast invertase have been concerned only with the external enzyme (a mannan protein which is localized in the cell wall), but recently it has been reported that the invertase inside the cytoplasmic membrane is a smaller form. This paper presents a comparative study of the distribution of invertase isozymes in two stains of yeast and, after the selection of the best conditions and source, the purification of the internal or small enzyme. The major purification is obtained by chromatography on diethylaminoethyl Sephadex, although ammonium sulfate precipitation and gel filtration in Sephadex G-200 are also used to separate the large and small enzymes. The purified internal invertase is homogeneous on the basis of chromatographic criteria and its behavior in the analytical ultracentrifuge. The molecular weight of the enzyme is approximately 135,000, and the specific activity is 2,900 units per mg of protein.