The invention provides a recombinant Escherichia coli host cell for producingan Escherichia coli L-asparaginase II enzyme. The host cell includes an Escherichiacoli chromosome and at least one copy of a recombinant extrachromosomal vector,wherein the recombinant extrachromosomal vector encodes the L-asparaginaseII enzyme, wherein the host cell chromosome also encodes the same L-asparaginaseII enzyme, and wherein the host chromosome does not encode any other isoform ofL-asparaginase II.