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Appl. Environ. Microbiol., Sep 1997, 3412-3418, Vol 63, No. 9
RM Verhaert, AM Riemens, JM van der Laan, J van Duin and WJ Quax
Alcaligenes faecalis penicillin G acylase is more stable than the
Escherichia coli enzyme. The activity of the A. faecalis enzyme was not
affected by incubation at 50 degrees C for 20 min, whereas more than 50% of
the E. coli enzyme was irreversibly inactivated by the same treatment. To
study the molecular basis of this higher stability, the A. faecalis enzyme
was isolated and its gene was cloned and sequenced. The gene encodes a
polypeptide that is characteristic of periplasmic penicillin G acylase
(signal peptide-alpha subunit-spacer-beta subunit). Purification,
N-terminal amino acid analysis, and molecular mass determination of the
penicillin G acylase showed that the alpha and beta subunits have molecular
masses of 23.0 and 62.7 kDa, respectively. The length of the spacer is 37
amino acids. Amino acid sequence alignment demonstrated significant
homology with the penicillin G acylase from E. coli A unique feature of the
A. faecalis enzyme is the presence of two cysteines that form a disulfide
bridge. The stability of the A. faecalis penicillin G acylase, but not that
of the E. coli enzyme, which has no cysteines, was decreased by a
reductant. Thus, the improved thermostability is attributed to the presence
of the disulfide bridge.
Copyright © 1997, American Society for Microbiology
Molecular cloning and analysis of the gene encoding the thermostable penicillin G acylase from Alcaligenes faecalis
Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, The Netherlands.
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