Intracellular pH topography: determination by a fluorescent probe.

The distribution of pH inside the yeast Endomyces magnusii was measured at 1 micron resolution using different external pH values. In a neutral buffer the pH of the cytoplasm was 6.7-7.2 in the center, decreasing to 6.0 toward the periphery of the cell. A decrease of external pH was followed by a gradual uniform decrease of internal pH. Using a comparison of the 'pH map' with phase-contrast picture of the same cell, the pH of the vacuoles was estimated to be 5.5-5.6.