An investigation into the feasibility of using azide-insensitive ATPase and ConA as yeast plasma membrane markers

Immunological evidence for the involvement of cell wall proteins in phosphate uptake in the yeast Saccharomyces cerevisiae

Immunological cross-reactivity between cell wall proteins obtained from two yeast genera (Candida tropicalis and Saccharomyces cerevisiae) is reported. Specific retention of two cell wall proteins from Saccharomyces cerevisiae by an immunoabsorbent column coupled with antibodies against phosphate binding protein 2(PiBP2) from Candida tropicalis allowed to generate antibodies against the proteins from S. cerevisiae. These antibodies were effective in inhibiting phosphate uptake by S. cerevisiae cells. The proteins from S. cerevisiae displayed a phosphate binding activity which was inhibited in the presence of the forementioned antibodies. These results and the observation that the amount of these proteins in the shock fluid was dependent of the growth conditions (i.e., in the presence or in the absence of phosphate) support the idea that these proteins are involved in the high affinity phosphate transport system.

Phosphate uptake in the yeast Candida tropicalis: purification of phosphate-binding protein and investigations about its role in phosphate uptake

The purification of a phosphate-binding protein (PiBP2) by immunoadsorption is described. The entire anti phosphate-binding protein 2 antibodies as well as the Fab fragments obtained from these antibodies inhibit Pi uptake by whole cells. The inhibition is a mixed type of inhibition (Vm and Km are affected). These results should be regarded as a possible involvement of phosphate-binding protein 2 in Pi uptake. The binding of 125I-labelled fragments prepared from anti phosphate-binding protein 2 antibodies to whole cells, to shocked cells and to protoplasts has been investigated. The results confirm the release of phosphate-binding protein by osmotic shock and during protoplast formation. From these findings, a cell-wall localisation, near the cell surface of the phosphate-binding protein should be proposed.

Identification of a plasma membrane protein involved in Pi transport in the yeast Candida tropicalis

A plasma membrane protein was found to contain antigenic determinants in common with a Pi-binding protein released by osmotic shock from Candida tropicalis. This plasma membrane protein (M.P. 30) has a molecular mass of 30 kDa as measured by SDS-PAGE and anti-M.P. 30 antibodies inhibit Pi uptake in protoplasts while only the corresponding Fab fragments inhibit Pi transport in whole cells. This plasma membrane protein may be the Pi plasma membrane carrier.