PRODUCTION OF N-15-LABELED HEN EGG-WHITE LYSOZYME USING ASPERGILLUS-NIGER

Aspergillus niger has been used as a host organism for the production of N-15-labelled hen egg white lysozyme (HEWL). In order to achieve maximum incorporation of label, strains expressing the HEWL gene were grown in medium containing ammonium N-15 chloride as sole nitrogen source. Yields of HEWL protein were reduced relative to those obtained on more complex media. Gains in yield using complex media were offset by reduction in N-15 incorporation. No differences in either yield or kinetics of production were observed when ammonium N-15 chloride was replaced by unlabelled ammonium chloride as sole nitrogen source. Yields of N-15-HEWL produced in this way are adequate for, and offer considerable advantages to, NMR studies of structure and folding of mutant and wild-type lysozymes.