Journal of Lipid Research, Vol 32, 1667-1673, Copyright © 1991 by Lipid Research, Inc.
Purification, characterization, and ontogeny of acetyl-CoA carboxylase isozyme of chick embryo brain
KG Thampy and AG Koshy
Fort Wayne Center for Medical Education, IN.
Acetyl-CoA carboxylase catalyzes the first committed step in the synthesis
of fatty acids. Because fatty acids are required during myelination in the
developing brain, it was proposed that the level of acetyl-CoA carboxylase
may be highest in embryonic brain. The presence of acetyl-CoA carboxylase
activity was detected in chick embryo brain. Its activity varied with age,
showing a peak in the 17-18-day-old embryo and decreasing thereafter. The
enzyme, affinity-purified from 18- day-old chick embryo brain, appeared as
a major protein band on polyacrylamide electrophoresis gels in the presence
of sodium dodecyl sulfate (Mr 265,000), indistinguishable from the 265 kDa
isozyme of liver acetyl-CoA carboxylase. It had significant activity (Sp
act = 1.1 mumol/min per mg protein) in the absence of citrate. There was a
maximum stimulation of only 25% in the presence of citrate.
Dephosphorylation using [acetyl-CoA carboxylase] phosphatase 2 did not
result in activation of the enzyme. Palmitoyl-CoA (0.1 mM) and malonyl- CoA
(1 mM) inhibited the activity to 95% and 71%, respectively.
Palmitoylcarnitine, however, did not show significant inhibition. The
enzyme was inhibited (greater than 95%) by avidin; however, avidin did not
show significant inhibition in the presence of excess biotin. The enzyme
was also inhibited (greater than 90%) by antibodies against liver
acetyl-CoA carboxylase. An immunoblot or avidin-blot detected only one
protein band (Mr 265,000) in preparations from chick embryo brain or adult
liver. These observations suggest that acetyl-CoA carboxylase is present in
embryonic brain and that the enzyme appears to be similar to the 265 kDa
isozyme of liver.
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