Prof. Todd D. Porter

My laboratory is interested in the regulation and activity of enzymes involved in cholesterol synthesis. We use biochemical and recombinant DNA techniques to express and characterize these enzymes and associated proteins in E. coli and in cultured hepatoma cells. We are particularly interested in how their activity is regulated at the protein level by regulatory proteins (kinases and accessory protein factors) as well as how sterols and botanical products can modulate their activity. Current studies are directed at understanding how garlic, tea, and policosanol (a by-product of sugar cane processing) inhibit cholesterol synthesis. General areas of interest include structure-function relationships of proteins, nutritional biochemistry, and molecular toxicology.

Biochemistry of the cytochrome P450 system, with emphasis on the structure and function of NADPH-cytochrome P450 reductase, the electron donor protein for this system, including studies on nitrosamine activation by CYP2E1 and P450 activity in P450 reductase-null mice.

Squalene monooxygenase requires an electron transfer partner as a source of electrons, and this redox partner has traditionally been thought to be NADPH-cytochrome P450 reductase (CPR). Recent studies with mice that lack hepatic expression of CPR indicate that a second electron donor may be present in liver cells, and that this protein may support up to 40% of the activity of squalene monooxygenase. Current studies are directed at identifying and characterizing this unknown electron transfer protein.
Mice that lack hepatic CPR expression develop fatty livers, consisting predominantly of triglycerides. It is not clear why loss of CPR expression would cause this lipidosis, as a role for CPR in triglyceride synthesis and processing has not been discovered. CPR is involved in both the synthesis and degradation of cholesterol, and so the connection may lie in disruption of this lipid homeostasis. We have replicated this lipidosis in hepatoma cell culture using an siRNA approach, facilitating investigation into this interesting and unexpected observation.

Ames mutagenicity assays with CYP2E1 and P450 reductase expressed in Salmonella tester strains.