Purification and identification of inactive forms of repressible and constitutive acid phosphatase in yeast

Acid phosphatase (EC 3.1.3.2, orthophosphoric-monoester phosphohydrolase, (acid optimum)) from the budding yeast Saccharomyces cerevisiae was purified from repressed and depressed cells. Without Triton X-100 in the extraction buffer only the constitutive or repressible active enzyme eluted from a Sepharose CL-6B column, the last step of the purification procedure. When Triton X-100 was included in the extraction buffer, an additional protein peak eluted prior to the active acid phosphatase. The material from this new peak, a glycoprotein, had no acid phosphatase activity but cross-reacted with antibodies raised against repressible acid phosphatase. The tryptic fingerprints of the inactive proteins are very similar to the ones of the corresponding active enzymes. We conclude that this new glycoprotein represents an inactive form of repressible and constitutive acid phosphatase. The fact that inactive acid phosphatase can be recovered only in the presence of Triton X-100 indicates that it is membrane-bound.