1. Structural changes of surface membrane of Plgsarum polycephalum were studied by examining the amount of 14C-p-chloromercuribenzoate or 125I bound to plasmodia and the molecular weight distribution of the labelled materials on SDS polyacrylamide gel electrophoresis.
2. By receiving the repellents such as fructose, NaCl, CaCl2 and LaCl3, the functional groups of the membrane reactable to 14C-PCMB or 125I were increased, while they were decreased appreciably under the presence of the attractants such as glucose, NaH2PO4, c-AMP and Ca (H2PO4) 2 in the concentration range around the respective thresholds for chemotaxis.
3. By eliminating the salt stimuli from the external medium, part of the macromolecules exposed on the surface membrane were released into the external medium, and they were supplied from the interior of the cell by adding the salt stimuli again.
4. EDTA-treatment of the plasmodium which had been found to modify the positive chemotaxis caused a structural change of the membrane involving the release of the membrane macromolecules.
