Ulrich Groeger

Papain‐catalyzed synthesis of dipeptides

Abstract The cysteine proteinase papain (EC 3.4.22.2) was used to synthesize N‐protected dipeptides in a kinetically controlled reaction starting from N‐benzyloxycarbonyl‐L‐alanine methylester as the carboxyl component. Beside L‐amino acid amides, free L‐amino acids could be successfully applied to yield the corresponding Z‐dipeptides. The yields with free L‐amino acids ranged from 13–80%, obviously depending on the structure of the molecule. The evaluation of the reaction conditions for the synthesis of N‐benzyloxycarbony1‐L‐alanyl‐L‐arginine revealed that a pH of 9.5, a temperature of 25–40°C and 0.5 M L‐arginine were optimal.

Microbial production of l-leucine from α-ketoisocaproate by Corynebacterium glutamicum

SummaryA process for l-leucine production was studied using Corynebacterium glutamicum for the conversion of α-ketoisocaproate. When this precursor was added to the culture medium in a concentration of 20 g/l about 16 g/l l-leucine were formed after a fermentation time of 57 h and the molar yield was 91%. Using a fed-batch culture it was possible to produce 24 g/l of l-leucine from 32 g/l of α-ketoisocaproate within 23 h. Enzymatic studies indicate that in this glutamate-producing bacterium α-ketoisocaproate is converted into l-leucine via the transaminase B reaction and l-glutamate is regenerated by the glutamate dehydrogenase. By the addition of α-ketoisocaproate to the culture medium the specific activity of transaminase B was increased threefold.