THE pufQ GENE REGULATES ACTIVITY INCREASES IN TWO ENZYMES OF PROTOPORPHYRIN IX SYNTHESIS IN RHODOBACTER CAPSULA TVS

摘要

The first gene of the pufopemn of Rhodobacter capsulatus (pufQ) encodes a 74-residue protein known to reside in the intracytoplasmic membrane (Fidai et al 1994). PufQ was first proposed to be involved in the regulation of bacteriochlorophyll (Bchl) biosynthesis by Bauer et al (1988), PufQ is apparently not required for or involved in the RegA/RegB or CrtJ regulatory systems. A puf-operon-deletion mutant that formed only a very small amount of Bchl was found to induce anaerobic transcription of the puc operon (regulated by RegA/RegB and CrtJ) normally (Forrest et al 1989). Rather than regulating bch genes (which are aerobically repressed by CrtJ), previous work in our laboratory (Fidai et al 1995, Smart et al 1998) has indicated that PufQ is involvedin the regulation of one or more hem gene(s). These genes encode enzymes catalyzing the conversion of 8-aminolevulinic acid (ALA) to protoporphyrin IX (Proto) during the early part of the Bchl biosynthetic pathway. We report herein the effect of the interruption or deletion of pufQ on Bchl content and the semiaerobic induction of increased activity in two enzymes of Proto synthesis, porphobilinogen (PBG) synthase and coproporphyrinogen III (Coprogen) oxidase. We have also carried out a kinetic analysis of PBG synthase and studied inhibition of the enzyme by two downstream metabolites, Coprogen and uroporphyrinogen III (Urogen).