Occurrence of specific sterols in Pneumocystis carinii.

We have examined the sterol composition and biosynthesis of rat Pneumocystis carinii. We found a number of lipid components among the nonsaponifiable fraction that appear unique to P. carinii. These lipids are present in P. carinii purified preparations and P. carinii-infected whole lungs but absent from control lungs. They show chromatographic properties typical of sterols on GC and HPLC; they are present in free and esterified sterol fractions isolated by thin layer chromatography, they are precipitated by digitonin and they are labeled upon incubation of purified P. carinii cell suspensions with [3H] mevalonate and [3H] squalene. The finding of these sterols opens new opportunities for the identification of chemotherapeutic targets against P. carinii.