Acid-stable microbial enzymes

Genes of different human digestive ennrmes u well m Ihiue nf several acid-stable microbial enzymes have been cloned and expressed. Some survive gastric proteolytic and acid denaturation and maintain their enzymatic activity in... 

Genes of different human digestive enzymes as well as those of several acid-stable microbial enzymes have been cloned and expressed. Some survive gastric proteolytic and acid denaturation and maintain their enzymatic activity in the complex physiological microenvironment of the lumen of the small intestine, being mainly conditioned by pH and bile acids [108-110], They may be useful in the therapy to pancreatic insufficiency, but require confirmation of clinical efficacy in carefully designed protocols in different age groups. 

We attempted continuous production of L-aspartic acid from fumaric acid and ammonia by immobilized Escherichia coli having high aspartase activity [3, 4, 5]. Various methods were tested for the immobilization of microbial cells, and a stable and active enzyme system was obtained by entrapping whole microbial cells in a polyacrylamide gel lattice. 

Conventional processing of food raw materials, as well as culinary methods used during food preparation, does not usually cause a significant isomerisation (racemisation) of L-amino acids (Table 2.25) (with the exception of aspartic acid), l-Aspartic acid and L-serine undergo racemisation relatively easily. L-lsoleucine (isomerises to D-flHo-isoleucine), L-prohne, L-threonine (isomerises to D-allo-threonine) and L-vahne yield smaller amounts of o-isomers. Free amino acids are roughly ten times more stable than amino acids bound in proteins. An extensive racemisation of amino acids does however occur, even at relatively low temperatures, in alkaline media used to inactivate enzymes, microorganisms, microbial... 

Lipases used for FAAE production are normally of microbial origin, such as CALB and TLL lipase. They are often used in immobilized forms, which are more stable and versatile than their free forms (Shimada et al, 2002 Kojima et al, 2004 Nielsen et al, 2008). The immobilized form is also more industrially feasible, as they can be easily packed and reused in industrial reactors. Nevertheless, they are also more costly in terms of enzyme price (per kg of immobilized enzyme). However, the stable and reasonably high productivity of the enzyme (kg of biodiesel/kg of immobilized enzyme) during a relatively long lifetime is more important than the sole price comparison. Whole-cell biocatalysts which are cheaper and more robust may be appropriate for industrial FAAE production (Antczak et al, 2009). The activity of whole-cell biocatalysts depends on the fatty acid composition of the cell wall membrane. As there may be different Upases bound to the cell waU or membrane, the FAAE yield may vary (Adamczak et al, 2009). 

---