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Todd D. Porter, Ph.D.

Research Topics

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.  

Our studies have focused on a key enzyme in the downstream pathway for cholesterol synthesis, squalene monooxygenase.  This enzyme is located on the endoplasmic reticulum of most cells and appears to have an important role in regulating the downstream pathway for cholesterol synthesis.  The activity of this enzyme is regulated by 'supernatant protein factor' (SPF), a lipid-binding cytosolic protein that may serve as a rapid-response modulator of cholesterol synthesis.  Current studies on this system using cell culture, purified enzymes, and subcellular preparations from whole animals may elucidate new mechanisms by which cholesterol synthesis is regulated.  

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.

Earlier studies on the coexpression of human cytochrome P450 2E1 with cytochrome P450 reductase in bacteria allowed the generation of an active mammalian monooxygenase system in these microorganisms.  This approach was taken to develop a recombinant Ames test that can replace the rat liver homogenate that is traditionally used to activate chemicals in this widely used mutagenicity assay.  Several bacterial expression and coexpression vectors have been developed for these enzymes, and are available upon request.  Maps and sequences can be obtained here.

There are presently over 200 mammalian P450 sequences known.  The codon usage of these genes varies greatly, and appears to correlate with the G-C content of that part of the genome in which they are located.

Squalene Monooxygenase


P450 Reductase


CYP2E1 Recombinant Ames Test


P450 Codon Usage


Plasmid Maps


Information for prospective students

Porter laboratory members

Comments to Todd D. Porter, Pharmaceutical Sciences, University of Kentucky College of Pharmacy, Lexington, KY 40536-0082.
Phone 859 257-1137; FAX 859 257-7564
Last Modified: October 08, 2004
Copyright 2000, University of Kentucky Chandler Medical Center