Purification, characterization, and kinetic mechanism of S-adenosyl-L-methionine:macrocin O-methyltransferase from Streptomyces fradiae

J Biol Chem. 1988 Oct 25;263(30):15619-25.


S-Adenosyl-L-methionine:macrocin O-methyltransferase catalyzes conversion of macrocin to tylosin, the terminal and main rate-limiting step of tylosin biosynthesis in Streptomyces fradiae. The O-methyltransferase was stabilized in vitro and purified to electrophoretic homogeneity. The purified enzyme had a molecular weight of 65,000 and consisted of two identical subunits of 32,000 with an isoelectric point of 4.5. The enzyme required Mg2+, Mn2+, or Co2+ for maximal activity and was catalytically optimal at pH 7.5-8.0 and 31 degrees C. The O-methyltransferase catalyzed the conversion of macrocin to tylosin at a stoichiometric ratio of 1:1. The enzyme also mediated conversion of lactenocin----desmycosin. The corresponding Vmax/Km ratios for the two analogous conversions were similar, and both enzymic conversions were susceptible to extensive competitive and noncompetitive inhibitions by macrolide metabolites. Steady-state kinetic studies for initial velocity, substrate analogue, and product inhibitions have allowed formulation of Ordered Bi Bi as the reaction mechanism for macrocin O-methyltransferase.

MeSH terms

  • Amino Acids / analysis
  • Chemical Phenomena
  • Chemistry
  • Cobalt / metabolism
  • Hydrogen-Ion Concentration
  • Kinetics
  • Leucomycins / metabolism
  • Magnesium / metabolism
  • Manganese / metabolism
  • Methyltransferases / isolation & purification*
  • Methyltransferases / metabolism
  • Molecular Weight
  • Streptomyces / enzymology*
  • Tylosin


  • Amino Acids
  • Leucomycins
  • Cobalt
  • Manganese
  • Methyltransferases
  • S-adenosyl-L-methionine-macrocin O-methyltransferase
  • Magnesium
  • Tylosin