Reaction mechanism, Candida

Although there are notable exceptions as given below, the most common lipase-catalyst used for polyester synthesis is Candida antarctica lipase B (CALB) (please refer to Chapter 14 for more information on the structure and reaction mechanisms of CALB). The immobilized CALB catalyst that has been primarily used is Novozym 435, manufactured by Novozymes (Bagsvaerd, Denmark). Novozym 435 consists of CALB physically adsorbed within the macroporous resin Lewatit VPOC 1600 (poly[methyl methacrylate-co-butyl methacrylate], supplied by Bayer) (please refer to Chapter 3 for more information on Novozym 435). 

Martin JC, BeUo JF, Buigmllo FJ, Roig MG. 1994. Kinetic behaviour and reaction mechanism of the hydrolysis of p-nitrophenyl palmitate in mixed micelles with Triton X-100 ceittilyzed by lipase from Candida rugosa. J Mol Catal 93 37—52. 

Shyadehi AZ, DC Lamb, SL Kelly, DE Kelly, W-H Schunck, JN Wright, D Corina, M Akhtar (1996) The mechanism of the acyl-carbon bond cleavage reaction catalyzed by recombinant sterol 14a-demethyl-ase of Candida albicans (other names are lanosterol 14a-demethylase, P-450]4p, and CYP51). J Biol Chem 271 12445-12450. 

As evident from Fig. 8.4, an increase in the selectivity has been observed in IL/ scCOj biphasic systems media (>99.5%) with respect to scCO assayed alone (95%). These results could be explained by the use of water-immiscible ILs which have a specific ability to reduce water activity in the enzyme microenvironment. The synthetic activity of the immobilized lipase in IL/scCO biphasic systems is lower than that in scCO assayed alone. Similar results were found by Mori et al. [40] in IL/ hexane biphasic systems. These authors reported that the enzymatic membranes prepared by simple adsorption of CaLB onto the surface were more reactive than membranes prepared with ILs. As can be observed in Fig. 8.4, the initial reaction rate in the assayed IL/scCO biphasic systems increased in the following sequence [bdimim ][PF ]<[bmim ][PFg ]<[bmim ][NTfj ]<[omim ] [PF ], which was practically in agreement with flie activity sequence reported by these authors using free Candida antarctica lipase B in homogeneous ionic liquid systems ([bmim ] [PF ]<[bdmim+][PFg ]<[bmim+][NTfj ]<[omim ][PF ]), with the exception of [bmim [PF ] and [bdimim+][PFg ]. These results were explained taking into account that biotransformation occurs within the ionic liquid phase, so substrates have to be transported from scCOj to the ionic liquid phase. The mechanism of substrate transport between the ionic liquid and the supercritical carbon dioxide could be by three consecutive steps diffusion of the substrates through the diffusion... 

Clearly it is incorrect to consider the nonoxidative phase of the P.p.c. as a fixed, albeit fairly complex mechanism for the conversion of 3 molecules of pentose phosphate into a triose phosphate and 2 molecules of hexose phosphate. There exists a network of possible reactions, which can change in emphasis, depending on the tissue, and possibly on the physiological state of the tissue. Thus, in rat epididymal fat pad, isotopic labeling suggests that the older scheme of Horecker operates for the metabolism of pentose phosphates. Operation of the new scheme in plants would provide an explanation of the Gibbs effect (see). Other workers [T.Wood A. Gascon Archives of Biochemistry and Biophysics 2Q3 (1980) 727-733] have reported their failure to demonstrate the interconversion of D-arabinose S-phosphate and D-ribose S-phosphate, or the role of D-arabinose S-phosphate as an acceptor for transketolase in baker s yeast, Candida ulilis, or rat liver. 

---