التفاصيل البيبلوغرافية
| العنوان: |
Biosynthèse de la chaîne latérale éthyle du stigmastanol et du stigmastè-22,ol-3β du myxomycète Dictyostelium discoïdeum. |
| المؤلفون: |
Ellouz, Radhouane, Lenfant, Maryse |
| المصدر: |
European Journal of Biochemistry; 1971, Vol. 23 Issue 3, p544-550, 7p |
| مصطلحات موضوعية: |
DICTYOSTELIUM discoideum, DICTYOSTELIUM, ETHYLENE dichloride, METHYLATION, ALKYLATION, BIOCHEMISTRY |
| مستخلص: |
Several laboratories have shown that the two carbon atoms C-28 and C-29 of the ethyl or ethylidene side chains of phytosterols are introduced on to a C-24 unsaturated side chain by two methylation steps. A scheme based on previous work suggests the various intermediates which can be formed by stabilisation of the carbonium ion 3. We have shown previously that in the biosynthesis of 5α-stigmastan-3β-ol (11α)and 5α-stigmast-22-en-3β-ol (12α), sterols of the myxomycete Dictyostelium discoideum, routes h and i could be excluded. In the present paper we describe the in vivo conversion, by the myxomycete, of differently labelled lanosterol (13), stigmastanol (11c), and 5α-stigmast-22-en-3β-ol (12c), into the sterols 12a and 11a, and discuss the possible biosynthetic routes for the two sterols. After incorporation of a mixture of [26,27-14C2]lanosterol and [24-³H]lanosterol (³H/14C = 5.60 ± 0.25), the isolated sterols 11a and 12a were converted into 11b (³H/14C = 5.54 ± 0,28) and 14b (³H14C = 5.61 ± 0.28). By ozonisation followed by oxidation in neutral or basic medium. 12a was converted into the esters 15 (³H/14C @ 5.54 ±0.28) and 16 (³H/14C 5.55 ± 0.3), respectively. These results show that during the C-24 methylation. H-24 is not lost: the hydrogen which is lost is located @9' neither at C-24 nor at C-23 and must therefore be at C-25. This excludes routes a and b for sterol 12. After incorporation of a mixture of 126,27-14C2]lanosterol and [23-³H]lanosterol (³H/14C = 4.36 ± 0.1) the isolated sterols 11a and 12a were converted into 11b (³H/14C = 4. 12 ± 0.2) and 14b (³H/14C = 3.32 ± 0.14); a fraction of 12b was degraded into 15 (³H/14C = 2.28 ± 0.31) and 16 (³H/14C= 3.44 ± 0.15). These results show that during the conversion of 13 into 12a, 50% of the H-23 atoms migrate from C-23 to C-24 and 25% remain on C-23 ; the other 25% are eliminated. During the conversion of 13 into 11a both H-23 atoms are retained. These results excluded route g for the two sterols. Since we have demonstrated that the conversion of 11c into 12a is possible in high yields (4 6%) with an efficiency eight times greater than the conversion of 12c into 11a, we propose that the sterol 11a is synthesized in vivo according to route e with migration of H-23 from C-23 to C-24. The sterol 12a is biosynthetized either by route d, f, the 22,23 double bond being introduced during the alkylation step, or by desaturation of the sterol 11a, the C-22 C-23 double bond being introduced after the C-24 alkylation. [ABSTRACT FROM AUTHOR] |
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| قاعدة البيانات: |
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