Comparison of antioxidant enzyme biosynthesis by free and immobilized Aspergillus niger cells☆

Effect of immobilization on antioxidant enzyme synthesis by growing and non-growing cell culture of Aspergillus niger 26 was studied. Entrapped cells showed a greater than 1.5-fold increase in the superoxide dismutase (SOD) activity and a moderate elevation in catalase activity. The immobilization did not cause changes in the spectrum of SOD isoenzymes. The observed increase in SOD activity required de novo synthesis of this enzyme, because it was suppressed by inhibitors of the transcription and translation. The addition of various viscous substances (agar, Na-alginate and pectin) stimulated the SOD synthesis. Despite these results, it was found that the changes in SOD activity are induced in response to growth in the state of immobilization rather than to presence of alginate. Immobilized A. niger cells exhibited about a 4- to 5-fold higher level of cyanide-resistant respiration. This latter phenomenon might use as an indicator of intracellular oxy-intermediate generation in cell culture growing under stress conditions. The results are discussed relative to association between physiological stress caused by immobilization and oxidative stress.