Mechanisms of the acido- and thermo-phily of Cyanidium caldarium Geitler II. Physiological role of the cell wall

1) A partially disintegrated cell preparation of Cyanidium caldarium(i.e. the 100G fraction; cells from which the outer parts ofthe cell wall had been removed) was obtained by differentialcentrifugation of a cell suspension treated with a French press.2) The 100G fraction cells had completely lost the outer partsof their cell walls, but retained their subcellular structureunchanged and had Hill activity that was equally as high asthat of the intact cells. 3) The Hill activity of the 100G fractionshowed an optimum at pH 7.0 and at 35°C. This activity waslost under acid and high temperature conditions (e.g. pH 3,50°C) under which intact cells showed high activity. 4)The Hill activity of the 100G fraction was lost by heat treatment(55°C, 10min), acid-treatment (pH 3.0, 10 min) or pre-illumination(3xl0⁵lux, 30 min) though intact cells were not inactivatedby these treatments. However, no remarkable difference in sensitivitytowards inhibitors was found between the 100G fraction and intactcells. 5) We thus concluded that the cell wall plays an importantrole in the acido- and thermo-phily of Cyanidium cells. (Received August 19, 1974; )