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1. Retinol exerted a remarkable stimulating effect (approx. 260% increase), essentially similar to that (300%) of phytol, on the so-called esterase activity displayed by crude pancreatic lipase [EC 3.1.1.3] toward true solutions of esters, but none of the typical lipase activity toward emulsions of water-insoluble esters. 2. Comparison of the stimulatory effects of retinol derivatives on the esterase activity revealed that retinyl acetate was the most active, being sustantially similar in effect to retinol; retinal was fairly active, while retinoic acid, retinyl palmitate, and beta-ionone were far less active. 3. With various isoprenoid compounds, the efficiency of stimulation increased with the carbon chain length, attaining a maximum at 15 to 20 carbon atoms. Above this chain length the efficiency decreased rapidly. 4. Comparison of the effects of retinol and phytol on the esterase activity of various other lipolytic enzymes indicated that this kind of activator may be relatively specific to porcine pancreatic esterase activity.

In the previous report, the residual fraction (residue) after extraction of fucosterol from the unsaponifiable matter of Hizikia fusiformis (hiziki) was found to possess essentially the same remarkable accelerating activity on pig pancreatic lipase as that of the unsaponifiable matter. Hence, the isolation and identification of the active principles from the residue were attempted, and the activity of three activators was investigated.One of the activators isolated from the residue was identified as phytol, a diterpene, by means of TLC and IR and MS spectrometry, thus providing the first demonstration of phytol in hiziki. Phytol, a new lipase-activator, was found to exhibit a more remarkable (250 to 300%) stimulating action than the residue itself (150 to 170%) on lipolysis when tested with triacetin as substrate.Other two activators, A-3 and A-9, isolated from the residue were suggested to belong to terpenes and sterols, respectively, and A-3 showed an activating effect essentially similar to that of phytol. Accordingly, some other terpenes (from different sources) were compared of their lipase-activating activity, and farnesol proved to be the most active, essentially to the same degree as phytol, but nerol, (3-carotene, and a-tocopherol to be far less active. Thus, the requirement for the optimal isoprene units in the activator molecule was suggested. (Received March 11, 1974)

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