Sunday, October 28, 2012

Regulatory Mechanisms- Lipid Metabolism

Enzyme
Pathway
Effect of substrate concentration
Allosteric Modification/ Fed back Inhibition
Induction/ Repression
Clinical Significance
Acetyl co A Carboxylase
Fatty acid synthesis
Activity increases during well fed state
Activity decrease during fasting
Activator-
Citrate,
ATP
Acetyl co A
Insulin-by causing de phosphorylation by stimulating protein phosphatase
Inhibitors-
Long chain fatty acids, Epinephrine, Glucagon- via changes in phosphorylation state through c AMP mediated phosphorylation cascade
Induced byInsulin

Repressed byGlucagon
Activity decreases in diabetes Mellitus
Carnitine Acyl Transferase
Carnitine shuttle
Activity low in fed state, high during fasting
Activated byGlucagon through lipolysis and provision of fatty acids for oxidation

Inhibited by insulin and malonyl co A

Inherited CAT-I deficiencyaffects only the liver, resulting in reduced fatty acid oxidation and ketogenesis, with hypoglycemia.
HMG co A Reductase
Cholesterol synthesis
Activity low in fasting state,
Activated by Insulin, Thyroid hormone

Inhibited by –Glucagon, Glucocorticoids,(By reversible phosphorylation)
Dietary cholesterol (Hepatic synthesis)
Mevalonate and cholesterol ,the products of pathway

Expression of HMG COA reductase is regulated by sterol regulatory element binding protein
Also induced by Insulin
Activity high in Diabetes mellitus die to availability of excess Acetyl co A.

Activity inhibited by Statins used as cholesterol lowering drugs.





------------------------------------------ Best Wishes: Dr.Ehab Aboueladab, Tel:01007834123 Email:ehab10f@gmail.com,ehababoueladab@yahoo.com ------------------------------------------
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