Overexpression of seven different genes restores growth of a ΔpdxB strain of E. coli, which cannot make pyridoxal phosphate (PLP), on M9/glucose.None of the enzymes encoded by these genes has a promiscuous 4-phosphoerythronate dehydrogenase activity that can replace the activity of PdxB.Overexpression of these genes restores PLP synthesis by three different serendipitous pathways that feed into the normal PLP synthesis pathway downstream of the blocked step.Reactions in one of these pathways are catalyzed by low-level activities of enzymes of unknown function and a promiscuous activity of an enzyme that normally has a role in another pathway; one reaction appears to be non-enzymatic.

Selection-amplification finds new RNA enzymes (ribozymes) among randomized RNAs with flanking unvaried sequences (primer complements). Precise removal of 3′-primer before reaction selected aminoacylation from PheAMP in 3 cycles, yielding active RNAs (k cat = 12-20 min -1 ) using only three conserved nucleotides, acting independently of divalent ions. This unusually simple RNA active site encouraged study of the reaction via molecular mechanics-based free energy minimization. On this basis, we suggest a chemical path for RNA-catalyzed transaminoacylation. Site modeling also predicted new features -L-stereoselectivity, 2′-regioselectivity, independence of amino acid side chain and phosphorylated activating group, that were subsequently verified. The same selection also showed that RNA aminoacylation from adenylate is simpler than from CoA thioester, potentially rationalizing translational activation by adenylates. The simplicity of this active site suggests a general route to small ribozymes.

Pyruvate is an important "hub" metabolite that is a precursor for amino acids, sugars, cofactors, and lipids in extant metabolic networks. Pyruvate has been produced under simulated hydrothermal vent conditions from alkyl thiols and carbon monoxide in the presence of transition metal sulfides at 250°C [Cody GD et al. (2000) Science 289(5483):1337-1340], so it is plausible that pyruvate was formed in hydrothermal systems on the early earth. We report here that pyruvate reacts readily in the presence of transition metal sulfide minerals under simulated hydrothermal vent fluids at more moderate temperatures (25-110°C) that are more conducive to survival of biogenic molecules. We found that pyruvate partitions among five reaction pathways at rates that depend upon the nature of the mineral present; the concentrations of H 2 S, H 2 , and NH 4 Cl; and the temperature. In most cases, high yields of one or two primary products are found due to preferential acceleration of certain pathways. Reactions observed include reduction of ketones to alcohols and aldol condensation, both reactions that are common in extant metabolic networks. We also observed reductive amination to form alanine and reduction to form propionic acid. Amino acids and fatty acids formed by analogous processes may have been important components of a protometabolic network that allowed the emergence of life.catalysis | prebiotic chemistry | abiogenesis B aross and Hoffman suggested in 1985 that life emerged in or around hydrothermal vents from a protometabolic network fueled by small molecules such as CO 2 , NH 3 , and H 2 in hydrothermal fluids (1). The existence of dense biological communities sustained solely by the chemicals and energy provided by vent fluids proves that these habitats are capable of supporting life. The possibility that life originated at such sites is appealing for a number of reasons. Pores in vent walls and the surrounding fractured crust could have provided compartmentalization before the availability of lipid membranes. The mineral surfaces lining these compartments could have catalyzed the formation of organic compounds from the constituents of vent fluids. Temperature gradients in hydrothermal systems could have allowed reactions with high activation energies to occur in the internal hot regions as well as formation of more fragile molecules near the cool outer wall. In addition, both theoretical and experimental studies have demonstrated that thermal gradients can lead to massive concentration of molecules in small regions of microchannels due to a combination of convection and thermophoresis (2, 3). This physical mechanism would enhance the rates of second-order reactions between molecules originating from chemical reactions in hydrothermal fluids as they percolate through pores and channels in vent structures and in cracks in the surrounding crust.An important challenge for prebiotic chemists is to explore the potential for synthesis of complex organic molecules from geochemical precursors in hydrothermal environments. In...

A reliable preparative-scale synthesis of 1-bromo-1-lithioethene is reported. This reagent undergoes clean 1,2-addition with a range of aldehydes and ketones at -105 degrees C to afford the corresponding 2-bromo-1-alken-3-ols in moderate to excellent yield. Efficient diastereoselective addition to alpha-siloxy and alpha-methylcyclohexanones, as well as protected 3-keto furanose sugars, is achieved in the presence of 10 mol % CeBr(3). The resulting bromoallylic alcohol adducts have considerable potential as synthetic building blocks. [reaction: see text]