Amino acid substitution enzyme

In many cases, the racemization of a substrate required for DKR is difficult As an example, the production of optically pure cc-amino acids, which are used as intermediates for pharmaceuticals, cosmetics, and as chiral synfhons in organic chemistry [31], may be discussed. One of the important methods of the synthesis of amino acids is the hydrolysis of the appropriate hydantoins. Racemic 5-substituted hydantoins 15 are easily available from aldehydes using a commonly known synthetic procedure (Scheme 5.10) [32]. In the next step, they are enantioselectively hydrolyzed by d- or L-specific hydantoinase and the resulting N-carbamoyl amino acids 16 are hydrolyzed to optically pure a-amino acid 17 by other enzymes, namely, L- or D-specific carbamoylase. This process was introduced in the 1970s for the production of L-amino acids 17 [33]. For many substrates, the racemization process is too slow and in order to increase its rate enzymes called racemases are used. In processes the three enzymes, racemase, hydantoinase, and carbamoylase, can be used simultaneously this enables the production of a-amino acids without isolation of intermediates and increases the yield and productivity. Unfortunately, the commercial application of this process is limited because it is based on L-selective hydantoin-hydrolyzing enzymes [34, 35]. For production of D-amino acid the enzymes of opposite stereoselectivity are required. A recent study indicates that the inversion of enantioselectivity of hydantoinase, the key enzyme in the... 

Dl. Daar, I. O., Artymiuk, P. J., Phillips, D. C and Maquat, L. E., Human triosephosphate iso-merase deficiency. A single amino acid substitution results in a thermolabile enzyme. Proc. Natl. Acad. Sci. U.S.A. 83,7903-7907 (1986). 

F5. Fujii, H., Krietsch, W. K. G., and Yoshida, A., A single amino acid substitution (Asp -> Asn) in a phosphoglycerate kinase variant (PGK Miinchen) associated with enzyme deficiency. J. Biol. Chem. 255,6421-6423 (1980). 

LHRH (see Fig. 6.16) is highly sensitive to proteolytic degradation. Enzymes with particular activity toward LHRH include angiotensin-converting enzyme, neprilysin, and thimet oligopeptidase (see Sect. 6.4.2 and Table 6.6). D-Amino acid substitution in position 6, 7, or 10 has led to the de-... 

Amino Acid Substitution The naturally occurring or experimentally induced replacement of one or more amino acids in a protein with another. If a functionally equivalent amino add is substituted, the protein may retain wild-type activity. Substitution may also diminish or eliminate protein function. Experimentally induced substitution is often used to study enzyme activities and binding site properties. [NIH]... 

This chapter aims to summarize our efforts to investigate the effects of fluorinated amino acid substitutes on the interactions with natural protein environments. In addition to a rather specific example concerning the interactions of small peptides with a proteolytic enzyme, we present a simple polypeptide model that aids for a systematic investigation of the interaction pattern of amino acids that differ in side chain length as well as fluorine content within both a hydrophobic and hydrophilic protein environment. Amino acid side chain fluoiination highly affects polypeptide folding due to steric effects, polarization, and fluorous interactions. 

The second part of the proof of colinearity of DNA and protein sequences was the determination of the complete amino acid sequence of tryptophan synthase and peptide mapping (Chapter 3) of fragments of the mutant enzymes. From the peptide maps it was possible to identify altered peptides and to establish the exact nature of the amino acid substitutions present in a variety of different tryptophan auxotrophs. When... 

Branched-chain aminotransferases (BCATs) evolved from aspartate aminotransferases (AATs) showed a record 105- to 2 x 106-fold improvement in catalytic efficiency (kcat/KM). Not only were the 13-17 amino acid substitutions concentrated in the most active mutants, but all but one mutated amino acid residues are located far from the active site. With directed evolution, enantioselectivities can be improved on enantiounspecific enzymes (from E = 1.1 to 25.8) and even inverted to yield the opposite enantiomer in comparison to the wild type (40% d- to both 90% d- and 20% L-). 

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