RESUMEN
AIMS: To demonstrate the presence of an active alpha-acetolactate decarboxylase in Streptococcus thermophilus and to investigate its physiological function. METHODS AND RESULTS: Streptococcus thermophilus CNRZ385 contains a gene encoding an alpha-acetolactate decarboxylase. Comparison of the production of alpha-acetolactate and its decarboxylation products, by the parent strain and an alpha-acetolactate decarboxylase-deficient mutant, demonstrated the presence of a control of the pool of alpha-acetolactate by valine, leucine and isoleucine. This control occurs via an allosteric activation of the alpha-acetolactate decarboxylase. Cell-free extracts of S. thermophilus were not able to decarboxylate the isoleucine precursor alpha-acetohydroxybutyrate. CONCLUSIONS: These results strongly suggest that one of the physiological functions of the alpha-acetolactate decarboxylase in S. thermophilus is to regulate leucine and valine biosynthesis by diverting the flux of alpha-acetolactate towards acetoin when the branched-chain amino acids are present at a high concentration. SIGNIFICANCE AND IMPACT OF THE STUDY: Regulation of branched-chain amino acid biosynthesis by alpha-acetolactate decarboxylase may occur in several other micro-organisms and explain some of their growth properties.
Asunto(s)
Aminoácidos de Cadena Ramificada/biosíntesis , Carboxiliasas/metabolismo , Regulación Bacteriana de la Expresión Génica , Streptococcus/enzimología , Acetoína/metabolismo , Carboxiliasas/genética , Medios de Cultivo , Diacetil/metabolismo , Hidroxibutiratos/metabolismo , Lactatos/metabolismo , Mutación , Streptococcus/genéticaRESUMEN
[reaction: see text] Diastereoselectivity of up to 88% was achieved for the synthesis of an alpha-mercapto gamma-unsaturated phosphonate using the readily available chiral dimenthylphosphonyl ester group and a carbanionic [2,3]-sigmatropic rearrangement. Absolute configuration of the newly formed chiral center of this nonracemic thiol was determined, and the corresponding phosphono thiolane and thiolane S-oxide were also stereoselectively prepared.
Asunto(s)
Antiinfecciosos/síntesis química , Organofosfonatos/síntesis química , Tiofenos/síntesis química , Espectroscopía de Resonancia Magnética , EstereoisomerismoRESUMEN
[reaction: see text]1,4-Hydrogen radical transfers can now be reliably envisaged in radical synthetic chemistry as demonstrated by the formation of the cyano derivative II from I. Due to related sequences involving this new translocation process, followed by a highly diastereoselective trapping of the resulting anomeric radical, access to intriguing enantiopure 1,2,3-triols such as III is available.