Andreas Karau

Deactivation of formate dehydrogenase (FDH) in solution and at gas-liquid interfaces.

Enzymes, increasingly important in the synthesis of fine chemicals and pharmaceutical intermediates, are often insufficiently stable under reacting conditions. We have investigated the stability, in homogeneous aqueous solution and at gas‐liquid interfaces, of formate dehydrogenase (FDH), important for cofactor regeneration, from Candida boidinii and overexpressed in E. coli. When exposed to mechanical stress, residual activity, [E]t/[E]0, and residual protein were found to scale proportionally with gas‐liquid surface area in the bubble column, verifying a surface‐driven process, and with time and total throughput in a gear pump, but did not seem to be influenced much by shear in a Couette viscometer. All FDH variants are deactivated by chaotropes but not kosmotropes: the first‐order deactivation constant kd correlates well with the Jones‐Dole coefficient B but not well with the surface tension increment Δσ of various concentrated ammonium salt solutions. This finding might provide guidance for focusing the search for quantitative theories of Hofmeister effects.

Amino Acids in Human and Animal Nutrition

Amino acids are key components of human and animal nutrition, both as part of a protein-containing diet, and as supplemented individual products. In the last 10 years there has been a marked move away from the extraction of amino acids from natural products, which has been replaced by efficient fermentation processes using nonanimal carbon sources. Today several amino acids are produced in fermentation plants with capacities of more than 100,000 tonnes to serve the requirements of animal feed and human nutrition. The main fermentative amino acids for animal nutrition are L-lysine, L-threonine, and L-tryptophan. DL-Methionine continues to be manufactured for animal feed use principally by chemical synthesis, and a pharmaceutical grade is manufactured by enzymatic resolution. Amino acids play an important role in medical nutrition, particularly in parenteral nutrition, where there are high purity requirements for infusion grade products. Amino acids are also appearing more often in dietary supplements, initially for performance athletes, but increasingly for the general population. As the understanding of the effects of the individual amino acids on the human metabolism is deepened, more specialized product mixtures are being offered to improve athletic performance and for body-building.