STEROLIC BIOMARKERS IN MARINE-PHYTOPLANKTON .1. FREE AND CONJUGATED STEROLS OF PAVLOVA-LUTHERI (HAPTOPHYTA)

Pavlova lutheri was examined for free and combined sterols. Eight comm on desmethylsterols represented more than 49% of the total sterols. Th e principal sterols of this group were poriferasterol, 5-ergostenol an d cholesterol. Four uncommon sterols were also detected: a methylstero l (4 alpha-methyl-24 beta-ethylcholest-22(23)-en-3 beta-ol) and three 4 alpha-methyldihydroxysterols (4 alpha-methylpavlovols). 4 alpha-Meth ylsterol is the dominant sterol and along with the pavlovols accounts for more than half the total sterols of P. lutheri. End products of st erol biosynthetic pathways were present in almost all forms, in contra st to intermediate products. The dominant 4 alpha-methylsterol occurre d exclusively in free form, in contrast to the pavlovols, which were p resent as glycoside conjugates only. This peculiar distribution and co njugation of sterols is discussed.