8. Polyketide Metabolites
• Polymerisation of acetate may result in the
formation of a fatty acid or a polyketide.
Polyketides result when a primer other than
acetate is included, and processing during
chain elongation results in the inclusion of
various other compounds. The chain may be
further processed by cyclisation, lactonisation,
or formation of thioesters or amides. The
result is a staggering number of possile
structures built from the simple primer units.
10. Aflatoxin
• Aflatoxins are produced in members of the
Aspergillus parasiticus group via the
polyketide pathway. The pathway has around
20 steps, and the end products include a
diversity of related compounds
(bisfuranocoumarins) that can be readily
converted one to another.
13. • Aflatoxins are toxic and carcinogenic.
• The LSD 50 for ducks is 0.33 mg/kg. At lower
levels and following prolonged exposure, the
toxins cause liver cancer in humans.
• Aflatoxin B1 is converted to Aflatoxin M (in
milk) on passage through cows. Though less
toxic, it does illustrate the potential damage
caused by consumption of contaminated
product.
16. Amino Acid Pathway
• Penicillin and cephalosporin are β lactam
antibiotics. β lactam antibiotics are produced
by a few Ascomycota and several bacteria.
• The precursors of these antibiotics are amino
acids. Synthesis of active antibiotics is
directed by the inclusion in the growth
medium of different organic and fatty acids
resulting in different side chains on the
compound.
19. Combination of Pathways
• Ergot alkaloids are synthesised from several
pathways. Trypotophan from the shikimic acid
pathway is attached to an isoprenoid moiety
from the mevalonate pathway, and several
amino acids from primary metabolism are added
depending on the final product. Ergot alkaloids
are produced as a complex mixture of related
compounds from a branched pathway.
• The activity of the alkaloids is as varied as the
compounds. In essence, the compounds may
function as vasodilators, hormone regulators,
and feeding deterrents. They can be active in
mammals and insects.