The effects of acyl-CoA derivatives (C8 to C20) on the activity
of the fatty acid synthetases from yeast and Corynebacterium
diphtheriae have been examined. Both enzyme
systems are inhibited by the longer chain acyl thioesters
(C16 to C20) and protected against this inhibition by bovine
serum albumin (BSA). Identical relief from acyl-CoA inhibition
is provided by the 6-0-methylglucose-containing
lipopolysaccharide (MGLP), from Mycobacterium phlei. It
is shown that MGLP forms a stable complex with palmitylCoA.
This interaction accounts for the BSA-like effects of
the polysaccharide. BSA and MGLP have two further effects
on the fatty acid synthetases under study, also attributable
to complex formation with palmityl-CoA. They
stimulate the rate of over-all synthesis from acetyl-CoA and
malonyl-CoAt and they cause a shift of the fatty acid pattern
towards products of shorter chain length. The observed effects
are discussed in terms of the regulation of fatty acid
synthesis both with respect to rate and product composition.
It is concluded that in the two microbial enzyme systems negative
feedback inhibition and its relief are important control
mechanisms
