Abstract
Cells of the ciliate Tetrahymena pyriformis GL overproduce and accumulate massive quantities of the heme intermediate, protoporphyrin IX. Protoporphyrin is localized intracellularly in discrete membranous compartments. The amount of porphyrin stored in the cell changes dramatically as cells progress through the growth cycle. Porphyrin overproduction is stimulated by delta-aminolevulinic acid, but only during the mid-stationary phase. Overproduction of protoporphyrin IX apparently results from an increase, late in the growth cycle, of activities subsequent to delta-aminolevulinic acid synthetase. Feedback inhibition in the pathway by accumulated protoporphyrin IX does not occur. The presence of Co2+ completely inhibits accumulation of protoporphyrin IX in a manner reversed by delta-aminolevulinic acid. Sn4+ stimulates protoporphyrin IX accumulation in the culture.
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