Assay of the possible organization of particle-bound enzymes with squalene synthetase and squalene oxidocyclase systems

Abstract

Lanosterol was biosynthesized in pig liver homogenate from [4,8,12-(14)C(3)]farnesyl pyrophosphate and [4S-4-(3)H]NADPH through the intermediary formation of squalene labelled asymmetrically with (3)H. The biosynthetic lanosterol, freed from labelled 24,25-dihydrolanosterol, which was also synthesized, was converted into 24,25-dihydrolanosteryl acetate and subjected to chemical degradations to locate the position(s) of the (3)H label in the molecule. The ratio of (3)H at C-11 to that at C-12 was found to be 1.28. Although a certain inequality of labelling was thus indicated, experimental uncertainties did not permit the conclusion that the asymmetrically labelled squalene might have been cyclized preferentially from one end.

Stereochemistry of trans-phytoene synthesis. Lycopersene as a carotene precursor and a mechanism for the synthesis of cis- and trans-phytoene

“…Several laboratories have investigated a similar problem-the randomization of squalene during sterol biosynthesis. By examining the distribution of in lanosterol synthesized from farnesyl pyrophosphate in the presence of NADP3H, Etemadi et al (1969) concluded that the biosynthesized squalene had randomized. Ebersole et al (1973) incubated (3i?…”

Free (S,S,)‐diaminopimelate is not an obligatory intermediate in lysine biosynthesis in Corynebacterium glutamicum

“…This is because diffusion through the cytoplasm would inevitably randomise an isotopic label originally present in only one of the homotopic groups, while a direct 'handing-on' process might prevent the rotation and preserve the original isotope labelling pattern. Such a stereochemical test for channelling was first proposed for squalene, as an intermediate in triterpene biosynthesis [S] but, in the cases examined, no conclusive evidence for 'handing-on' of squalene was found [6,7]. In contrast, the five-carbon chain in sedamine and related piperideine alkaloids appears to be derived from cadaverine that remains tightly enzyme-bound (perhaps via an imine linkage) [8].…”