Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P50583 (asymmetrical)
 12,197 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The steric course of the methyl group transfer catalyzed by catechol O-methyltransferase was studied using S-adenosylmethionine (AdoMet) carrying a methyl group made chiral by labeling with 1H, 2H, and 3H in an asymmetrical arrangement. Incubation of the two diastereomers of this substrate with catechol O-methyl-transferase purified from rat liver and epinephrine or protocatechuic acid as acceptor gave the corresponding methylated catechols. These were degraded to convert the methoxy group in a series of stereochemically unambiguous reactions into the methyl group of acetate, which was then analyzed for its configuration. The results indicate that the transfer of the methyl group from AdoMet to either acceptor occurs in an inversion mode. The catechol O-methyltransferase reaction thus involves a direct transfer of the methyl group from the sulfur of AdoMet to the oxygen of the catechol in an SN2 process, without a methylated enzyme intermediate.
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PMID:Stereochemical course of the transmethylation catalyzed by catechol O-methyltransferase. 699 10

On standing in organic solvents containing traces of water, C3 and C1 isomers of C60F36 slowly convert to C1 isomers of C60F35OH. Both fluorofullerenols eliminate HF during EI mass spectrometry to give C60F34O epoxides, one fullerenol being much less stable than the other to the extent that the mass spectrum shows only the epoxide. Both C60F35OH isomers have C1 symmetry, one being identified by the remarkable linear relationship between chemical shifts in its 19F NMR spectrum and those in the spectrum of C1 C60F36; the spectrum of the other shows the pattern of C3 C60F36 rendered asymmetrical by the replacement of one F by OH. The reactions are facilitated by the presence of isolated double bonds, and provide the first proven examples of an SN2' reaction of a fullerene derivative. Our observation explains why only a limited number of fluorines are readily replaced in C60F36 and why C60F18 is by contrast much more resistant to hydrolysis. We have isolated also a pure isomer of C60F36O, which is shown to be an oxahomofullerene (ether) apparently derived from C1 C60F36, and an impure fraction comprising a fourth isomer of C60F36, a trifluoromethyl derivative of C60F36, a second isomer of C60F36O, and an unknown species of 1392 u.
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PMID:In the first proven SN2' fullerene reaction, both C3 and C1 C60F36 hydrolyse to C1 isomers of C60F35OH that eliminate HF to give epoxides C60F34O; C60F36O oxides are shown to be ethers, and a fourth isomer of C60F36 exists. 1292 43