Enzymes involved in methane formation from carbon dioxide and dihydrogen in Methanopyrus kandleri require high concentrations (> 1 M) of lyotropic salts such as K2HPO4/KH2PO4 or (NH4)2SO4 for activity and for thermostability. The requirement correlates with high intracellular concentrations of cyclic 2,3-diphosphoglycerate (cDPG; approximately 1 M) in this hyperthermophilic organism. We report here on the effects of potassium cDPG on the activity and thermostability of the two methanogenic enzymes cyclohydrolase and formyltransferase and show that at cDPG concentrations prevailing in the cells the investigated enzymes are highly active and completely thermostable. At molar concentrations also the potassium salts of phosphate and of 2,3-bisphosphoglycerate, the biosynthetic precursor of cDPG, were found to confer activity and thermostability to the enzymes. Thermodynamic arguments are discussed as to why cDPG, rather than these salts, is present in high concentrations in the cells of Mp. kandleri.

A new synthetic procedure to methylethers has been developed by the reaction of alcohols with dimethylcarbonate, a non-toxic and environmentally friendly reagent. The methylation of alcohols is catalysed by alumina or hydrotalcite. The methylcarbonate formed in the first step undergoes decarboxylation in the second step, to give the corresponding methylether. The reactivity follows the order: primary > secondary ≫ tertiary alcohols. The reaction can be efficiently performed under both batch and continuous flow conditions

Dedicated to Professor Bernt Krebs on the occasion of his 60th birthdayThe search for new low-molecular weight catalysts is one of the most fascinating fields of contemporary organic chemistry. One source of inspiration is the spatial arrangement of functional groups in the active site of enzymes, that is the design and synthesis of enzyme models. [1, 2] Many enzymes harbor a metal ion in the active site. The success in modeling a metalloenzymeÐand in constructing a novel metal catalyst in generalÐheavily relies on the matching of the ligand(s) with the central metal ion and with the substrate. Although this problem is widely recognized, it was only recently that parallel ligand synthesis and rapid screening methods were introduced to the field of catalyst research. [3±6] Herein, we describe our approach to artificial hydrolase activity which consists of a) the split-mix synthesis [7] of a ligand library containing 625 solid-phase-bound undecapeptides, b) complexing of the ligand library with Lewis acidic transition metals, and c) screening of the library with chromogenic test substrates. As it turned out, solid-phasebound undecapeptides ligands could be identified that mediate the hydrolysis of phosphates. The sequences of the most active (and inactive) peptides were determined by means of Edman degradation, and the catalytic activity or inactivity could be confirmed in homogeneous solution.The general structure of our ligand library is shown in Figure 1. Initially Fmoc-l-Phe was attached to TentaGel S ± NH 2 by using PyBOP as the coupling agent (Fmoc 9-fluorenylmethoxycarbonyl). [8] After splitting the polymer PEG Phe X GlyGly X GlyGly X GlyGly X Figure 1. General structure of the undecapeptide library. PEG polyethylene glycol.

No abstract

Das kombinatorische Auffinden katalytischer Aktivität erfordert das Zusammenspiel von Bibliothekssynthese und geeigneten Assays. Mit dem Testsubstrat 1 wurden in einer Bibliothek Undecapeptide gefunden (z. B. A), die in Gegenwart von Zr4+ die Phosphathydrolyse beschleunigen.