REGULATION AND KINETIC MODELING OF GALACTOSE-OXIDASE SECRETION

Production of extracellular galactose oxidase by Fusarium sp. NRRL 290 3 appears to be best in medium containing L-sorbose, which acts as a p aramorphogen for several filamentous fungal species. Analysis of galac tose oxidase activity in culture supernatants and the occurrence of ga oA mRNA, during growth in media containing either L-sorbose or glycero l as the sole source of carbon, indicates that the two carbon sources result in high and low levels of extracellular galactose oxidase activ ity, respectively, which is in parallel with the level of transcriptio n. The influence of altering the carbon source for growth on the regul ation of galactose oxidase synthesis and secretion appears to be mainl y at the level of gene expression rather than pH or cell density, alth ough these factors are also known to have some regulatory effect on th e level of secretion. Kinetics of galactose oxidase secretion, evaluat ed on the basis of altering the pH of the growth medium, agrees with t he Luedeking-Piret equation and suggests that the growth associated an d the non-growth associated product formation rates are changed in exp ense of each other.