COS-1 cells have very low levels of endogenous CPT2 and correspondingly low rate

Question

COS-1 cells have very low levels of endogenous CPT2 and correspondingly low rates of mitochondrial fatty acid uptake and fatty acid oxidation. When COS-1 cells are transfected with a plasmid expressing the WT-CPT2 gene, fatty acid oxidation levels increased in proportion to the expression levels of the protein for low and moderate levels of expression. High levels of protein expression did not increase fatty acid oxidation above this maximal level. Two of the mutations examined (P50H and S113L) were expressed in COS-1 cells, and fatty acid oxidation rates were compared to WT-CPT2 at the same expression levels. These mutations showed about 20% of the rate of fatty acid oxidation as the WT protein. For P50H and S113L, increasing the amount of mutant protein expression by a factor of 5 compared to WT-CPT2 led to similar amounts of fatty acid oxidation. What kinetic parameter for the CPT2 reaction appears to be affected by these mutations? Why?

Explanation / Answer

The kinetic parameter affected is the process of feedback inhibition. The oxidation of fatty acids acts as a checkpoint in the cell. This property has been mutated. This might be due to the modification of the receptor on the molecule.When the receptor is modified, the enzyme can no longer bind and the reaction goes on.

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