Densitometric quantification of ether-type phospholipids.

A quantification method for analysis of individual ether-type phospholipids is important in studies of the regulation of membrane lipid biosynthesis in Archaea. For ester-type lipid of Bacteria and Eucarya, a densitometric method has been established for simultaneous quantification of individual phospholipids visualized with molybdenum blue reagent on a TLC plate. In this study, we developed a TLC densitometric method for rapid quantitative determination of 6 kinds of main ether-type phospholipids in a methanogenic archaeon and an extremely halophilic archaeon. It has been reported previously that on densitometric quantification the values of molar absorptivities are approximately the same among most ester-type phospholipids. On the other hand, we found significant disparity in the molar absorptivity of archaeal ether-type lipids and serine-containing ester-type lipid. Therefore, analysis should be accomplished by use of each standard mixture. Compared with a previous method (preparative TLC method) that is measurement of inorganic phosphate of silica gel powder scraped off from spots of phospholipids on a TLC plate, the TLC densitometry is accomplished at one tenth the sample size in a short time.