D Zorica Knezevic-Jugovic

Lipases as biocatalysts for biodiesel production.

Lipases can be used for a variety of biotechnological applications: synthesis of fine chemicals, therapeutics, agrochemicals, cosmetics, flavors, biopolymers and biodiesel. Biodiesel is an alternative fuel for diesel engines that is environmentally acceptable. Conventionally, biodiesel is produced by transesterification of triglycerides and short chain alcohols in the presence of an acid or an alkaline catalyst. There are several problems associated with this kind of production that can be resolved by using lipase as the biocatalyst. The usage of lipases has several advantages over the conventional chemical methods. It is considered as less energy intensive and environmentally friendly. However, there are two main obstacles associated with the effective utilization of lipases in the production of biodiesel. The main one is the cost of the enzyme and its poor stability in the presence of excess alcohol. Several strategies are proposed to overcome these drawbacks: immobilization of lipases, stepwise addition of alcohol, and the usage of novel acyl acceptors and the usage of whole cell biocatalysts.

Immobilization of alginate-PAC on Sepabeads EC-HA support

Penicillin acylase (PAC) is an important industrial enzyme for the production of many β-lactam antibiotics. It is capable of catalyzing the hydrolysis of penicillin G (Pen G) to generate phenylacetic acid (PAA) and 6-aminopenicillanic acid (6-APA). In this paper, in order to prevent enzyme inactivation, an attempt of coupling enzyme modification and immobilization was presented. Chemical modification was promoted to introduce carbohydrate moiety into the PAC molecule, capable of being covalently linked to an amino support. This seems to provide a possibility to couple the enzyme without risking a reaction at the active site which might cause a loss of activity. PAC molecules were modified by cross-linking with polyaldehyde derivatives of alginate in order to add them new and useful functions. Immobilization of alginate-PAC on Sepabeads EC-HA was used as a model system in order to demonstrate the potential of this strategy. Optimal conditions for covalent immobilization of alginate-PAC from Escherichia coli on support Sepabeads EC-HA, were investigated. The immobilized enzyme was then characterized by evaluating the potential effects of immobilization on its thermal stability, temperature and pH profile in comparison with native non-modified PAC and modified non-immobilized PAC. The maximum amount of the alginate-PAC coupled on the dry support of 99 mg/g was satisfactory. Deactivation rate constants at 50 oC for free PAC, alginate-PAC and alginate-PAC immobilized on Sepabeads EC-HA were 2,32; 50,65 and 1,68 h-1, respectively. Alginate-PAC and alginate-PAC immobilized on Sepabeads EC-HA had the same pH and temperature optimum as the native non-modified PAC.