Avermectin B2 O-methyltransferase activity in "Streptomyces avermitilis" mutants that produce increased amounts of the avermectins.
The level of activity of avermectin B O-methyltransferase, the enzyme which catalyzes the conversion of avermectin B components to avermectin A components, was analyzed in a series of "Streptomyces avermitilis" mutants selected for increased production of the avermectins. In all of the mutants, increased avermectin production was accompanied by increased avermectin B O-methyltransferase activity. Both the average specific activity and the maximum observed specific activity of avermectin B O-methyltransferase increased in direct proportion to avermectin production. The level of avermectin B O-methyltransferase alone did not determine the extent of conversion of avermectin B components to avermectin A components, since a constant ratio of B components to A components was maintained throughout the fermentation even though avermectin B O-methyltransferase specific activity varied three- to fivefold. These results indicate that avermectin B O-methyltransferase is not rate limiting. The correlation between avermectin B O-methyltransferase specific activity and avermectin production is compatible with the hypothesis that genes coding for successive steps in the same secondary metabolite biosynthetic pathway are coordinately regulated.
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Schulman
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Valentino
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Nallin
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Kaplan
D001426:Bacterial Proteins; D007559:Ivermectin / Q000031:analogs & derivatives*; D007700:Kinetics; D007783:Lactones / Q000378:metabolism*; D008780:Methyltransferases / Q000378:metabolism*; D012436:S-Adenosylmethionine / Q000378:metabolism; D013302:Streptomyces / Q000201:enzymology / Q000378:metabolism*
D001426:Bacterial Proteins; D007783:Lactones; D007559:Ivermectin; C019264:avermectin; D012436:S-Adenosylmethionine; C048379:AveD protein, Streptomyces avermitilis; D008780:Methyltransferases