INDUSTRIAL-DESIGN OF ENZYMATIC PROCESSES CATALYZED BY VERY ACTIVE IMMOBILIZED DERIVATIVES - UTILIZATION OF DIFFUSIONAL LIMITATIONS (GRADIENTS OF PH) AS A PROFITABLE TOOL IN ENZYME ENGINEERING

We have developed integrated studies of enzyme reaction engineering fo r the hydrolysis of penicillin G catalysed by very active penicillin G acylase (PGA) derivatives. We have studied the distinct effect of a k ey variable (pH) on different industrial parameters (e.g. activity/sta bility parameters). In this way we have demonstrated, in contrast with that proposed by other authors, that the generation of gradients of p H inside the porous structure of very active enzyme derivatives may be not a problem but a 'very profitable tool' to improve the whole set o f industrial parameters. In this way we can establish two distinct 'op timal pH values': (i) the one inside the particle of the biocatalyst a nd (ii) the one in the bulk solution. The use of an external pH of 8.0 associated with the promotion of a controlled decrease in internal pH (e.g. around a mean value of 5.5) was very useful to simultaneously o btain interesting values of all industrial parameters: (i) very high h ydrolytic yields (higher than 97%); (ii) a very important increase on the stability of PGA derivatives (higher than a 50-fold factor); and ( iii) a very small decrease in operational activity (similar to 15%) as compared with the one of soluble enzyme at pH 8.0 with no diffusional hindrances.