title: Preliminary characterization of ferrichrome synthetase from Aspergillus quadricinctus.
abstract: An enzyme synthesizing the cyclic hexapeptide, ferrichrome, was partially purified from extracts of Aspergillus quadricinctus by fractional (NH4)2SO4 precipitation and Bio-Gel A 1.5 m filtration. About a 20-fold purification was achieved. The enzyme system incorporated delta-N-acetyl-delta-N-hydroxyornithine into ferrichrome and catalyzed ATP-PP1 exchange reactions, dependent on the constituent amino acids, glycine and delta-N-acetyl-delta-N-hydroxyornithine, in the presence of Mg2+. The optimal temperature was 27 degrees C. Km values were 3.1 . 10(-4) M for glycine and 5.3 . 10(-6) M for delta-N-acetyl-delta-N-hydroxyornithine. Both Km values were significantly lowered in the presence of 1 . 10(-6) M Fe3+. From the inhibition experiments it is concluded that sulfhydryl groups of the enzyme are involved. Both monomers are covalently bound to the enzyme in the course of the reaction. A molecular weight of 1.1 . 10(6) was determined by gel filtration. As the partially purified protein fraction also catalyzed transacetylation of hydroxyornithine from acetyl CoA, the peptide synthesizing activity may be part of a multienzyme complex. No ferrichrome synthetase activity can be found when the fungus is grown in the presence of 1. 10(-5) M Fe3+.
mesh_terms: D000596:Amino Acids / Q000494:pharmacology; D001230:Aspergillus / Q000201:enzymology*; D004794:Enzyme Repression; D005285:Fermentation; D007501:Iron / Q000494:pharmacology; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008970:Molecular Weight; D009952:Ornithine / Q000031:analogs & derivatives; D010453:Peptide Synthases / Q000302:isolation & purification / Q000378:metabolism*; D013439:Sulfhydryl Reagents / Q000494:pharmacology
chemical_list: D000596:Amino Acids; D013439:Sulfhydryl Reagents; C029642:delta-N-acetyl-delta-N-hydroxy-L-ornithine; D007501:Iron; D009952:Ornithine; D010453:Peptide Synthases; C029612:ferrichrome synthetase; D008274:Magnesium