Pyrrolnitrin is a secondary metabolite derived from tryptophan and has strong antifungal activity. Recently we described four genes,prnABCD, from Pseudomonas fluorescens that encode the biosynthesis of pyrrolnitrin. In the work presented here, we describe the function of each prn gene product. The four genes encode proteins identical in size and serology to proteins present in wild-type Pseudomonas fluorescens, but absent from a mutant from which the entire prn gene region had been deleted. The prnA gene product catalyzes the chlorination of l-tryptophan to form 7-chloro-l-tryptophan. The prnB gene product catalyzes a ring rearrangement and decarboxylation to convert 7-chloro-l-tryptophan to monodechloroaminopyrrolnitrin. The prnC gene product chlorinates monodechloroaminopyrrolnitrin at the 3 position to form aminopyrrolnitrin. The prnD gene product catalyzes the oxidation of the amino group of aminopyrrolnitrin to a nitro group to form pyrrolnitrin. The organization of the prn genes in the operon is identical to the order of the reactions in the biosynthetic pathway.

The non-haem chloroperoxidase gene (cpoF) from the pyrrolnitrin producer Pseudomonas fluorescens BL914 was cloned using an oligonucleotide derived from part of the N-terminal amino acid sequence of chloroperoxidase (CPO-P) from Pseudomonas pyrrocina as a probe. Based on the overexpression of cpoF in Escherichia coli and the stabilty of CPO-F against higher temperatures and proteases, the enzyme was purified to homogeneity. Partial characterization of the enzyme showed that it belongs to the class of bacterial non-haem CPOs. To investigate the role of CPO-F in pyrrolnitrin biosynthesis, the cpof gene was inactivated by insertion of a kanamycin cassette. Exchange of the chromosomal cpoF gene against the disrupted copy had no influence on pyrrolnitrin production demonstrating that CPO-F was not involved in pyrrolnitrin biosynthesis.

The enzymatic reaction arylNH2→arylNO2, the nonenzymatic counterpart of which requires drastic conditions, was previously hardly studied. Now a chloroperoxidase (CPOP) isolated from the bacterial species Pseudomonas has been found to catalyze not only halogenations in vitro, but also the oxidation of the precursor 1 to 2.

Die enzymatische Reaktion Aryl‐NH2→‐Aryl‐NO2, deren nichtenzymatische Version drastische Bedingungen erfordert, war bisher kaum untersucht. Aus einem Bakterienstamm der Gattung Pseudomonas, der das Antibioticum Pyrrolnitrin 2 produziert, konnte eine Chlorperoxidase (CPO‐P) isoliert werden. Sie katalysiert in vitro nicht nur Halogenierungen, sondern auch die Oxidation der Vorstufe 1 zu 2.