The potential of pyridoxal-5-phosphate dependent tyrosine decarboxylase (E.C. 184.108.40.206) of
was explored for the biotransformation of L-tyrosine to tyramine. Maximum bioconversion of L-tyrosine to tyramine was achieved in tyramine production medium (pH −5.5) at 30 °C after 16 h of incubation with 0.2% L-tyrosine. The yield of tyramine was found to be 11.8 μg/mL by the growing cells of
at shake flask level. Growth medium and different physico-chemical parameters to maximize the biotransformation of L-tyrosine to tyramine were optimized and yielded 1.9-fold increased synthesis of tyramine.
In recent times, biotechnological applications of microbial lipases in synthesis of many organic molecules have rapidly increased in non-aqueous media. Microbial lipases are the ‘working horses’ in biocatalysis and have been extensively studied when their exceptionally high stability in non-aqueous media has been discovered. Stability of lipases in organic solvents makes them commercially feasibile in the enzymatic esterification reactions. Their stability is affected by temperature, reaction medium, water concentration and by the biocatalyst’s preparation. An optimization process for ester synthesis from pilot scale to industrial scale in the reaction medium is discussed. The water released during the esterification process can be controlled over a wide range and has a profound effect on the activity of the lipases. Approaches to lipase catalysis like protein engineering, directed evolution and metagenome approach were studied. This review reports the recent development in the field of non-aqueous microbial lipase catalysis and factors controlling the esterification/transesterification processes in organic media.
A wide range of fatty acid esters can be synthesized by esterification and transesterification reactions catalyzed by lipases in non-aqueous systems. In the present study, immobilization of a purified alkaline extra-cellular lipase of
MTCC 8372 by adsorption on diatomaceous earth (celite) for synthesis of ethyl acetate via transesterification route was investigated.
lipase was deposited on celite (77% protein binding efficiency) by direct binding from aqueous solution. Immobilized lipase was used to synthesis of ethyl acetate from vinyl acetate and ethanol in
-nonane. Various reaction conditions, such as biocatalyst concentration, substrates concentration, choices of solvents (
-alkanes), incubation time, temperature, molecular sieves (3Å × 1.5 mm), and water activity(a
), were optimized. The immobilized lipase (25 mg/ml) was used to perform transesterification in
-alkane(s) that resulted in approximately 73.7 mM of ethyl acetate at 55 °C in
-nonane under shaking (160 rpm) after 15 h, when vinyl acetate and ethanol were used in a equimolar ratio (100 mM each). Addition of molecular sieves (3Å × 1.5 mm) as well as effect of water activity of saturated salt solutions (KI, KCl and KNO
) to the transesterification efficiency has inhibitory effect. Batch operational stability tests indicated that immobilized lipase had retained 50% of its original catalytic activity after four consecutive batches of 15 h each.