Die chemische struktur der biosynthetischen vorstufe des squalens

Presqualenyl-pyrophosphate (PSPP) was synthesized from farnesyl-pyrophosphate (FPP). The purified product could be transformed into a squalene in 90% yield. The structure of PSPP was established by the following experiments:1) PSPP displays a remarkably acid-labile phosphate-ester bond. Analogous to FPP it was possible to stabilize this bond by the addition of bromine. This indicates a structure of the allylester type.2) On acid hydrolysis PSPP splits off not only the pyrophosphate but also water. This may be best explained by the presence of a tertiary hydroxyl group in PSPP.3) The pyrophosphate group of PSPP could be split by prostatic phosphatase. In gas-liquid-chromatography the trimethyl-silylated product gave a single peak. From the mass spectra of this compound and of the corresponding alcohol the expected molecular weight of 426 could be verified for the latter.4) Determining the 3H/(14)C ratio in 1-(3)H(2)-4(14)C-FPP and in PSPP and squalene, synthesized from it, only three 3H-atoms could be detected in PSPP and in squalene.5) Ozonisation of PSPP, synthesized from 1-(14)C-FPP, gave radioactive malondialdehyde, which was characterised as azobenzene-malondialdehyde and 4-azobenzene-1-phenyl-pyrazole. The experimental results are in agreement with the following structure of 2, 6, 10, 15, 19, 23-hexamethyl-n-tetracosa-2, 6, 11, 14, 18, 22-hexaen-10-yl-pyrophosphate for PSPP.

Crystallization of a multienzyme complex: fatty acid synthetase from yeast

The crystallization of purified fatty acid synthetase from yeast is facilitated by seeding techniques. The first seed crystals appeared as particles with almost negligible enzymatic activity in a solution that had been left at 4 degrees C for 15 months. Subsequently, the crystallization time has been reduced to two days, and the crystals now isolated have retained their full enzymatic activity. The loss of synthetase activity that can result from prolonged exposure during crystallization is attributable specifically to damage of the enzyme component responsible for condensation activity. Crystalline synthetase is identical to purified but noncrystalline synthetase by all criteria so far examined.

The role of biotin-dependent carboxylations in biosynthetic reactions

Images