Nomenclature and methodology for classification of nontraditional biocatalysis

Recent nontraditional biocatalytic techniques, particularly those which have involved introduction of enzymes into organic liquid phases, have revolutionalized the way we think about biocatalysis. Within the past decade, a variety of research programs and open literature publications have arisen investigating nonaqueous enzyme activities and the potential for using such processes commercially. However, because of the wide variety of reaction and reactor types possible, as well as vague and easily misinterpreted terminology, it is often difficult to ascertain which reaction configurations are being studied and how these maybe contrasted with similar research. We propose a systematic nomenclature and vocabulary such that reaction types can be quickly classified and compared with other nontraditional systems. The approach we have taken to distinguish between systems is primarily dependent upon the phase in which each of the critical reaction components (biocatalyst, reactant(s), and product(s)) is present. Possible resident phases include aqueous(A), organic (O), vapor (V), and supercritical (SC). With this system, a reaction scheme may be classified with a three-character identifier, such as AAO (a system in which the enzyme and substrate are present in an aqueous phase and the product is recovered from an organic phase). Special cases, such as when the biocatalyst is immobilized or the product forms an insoluble precipitate, are also discussed in the context of this nomenclature. This developed nomenclature and vocabulary also allow categorization of biocatalytic bioprocessing into two distinct classes: traditional (aqueous phase only) and nontraditional, the latter of which may be further subdivided into nonaqueous, aqueous, and supercritical biocatalysis. Such categorization provides a cohesive methodology by which to classify new work within the nontraditional arena, as well as to broaden or refine current research. Furthermore, this paper provides a technology roadmap which outlines nontraditional areas and their associated development issues which still require examination, in terms of both bridging and fundamental research, before these techniques will be adopted by the private sector.