Genetics and Biochemistry

Dr. Gary L. Powell

Gary Powell

Emeritus Professor

Ph.D. Chemistry
Purdue University

Contact Information
Phone: (864) 654-4188
Email: glpwl@clemson.edu

Research Focus Areas
Plant Genetics and Biochemistry
Protein Structure and Function

 

Research Activities

During my 37 years of active teaching and research at Clemson University (August, 1969 -  May, 2006) my research covered various areas.  I began my research in regulation of lipid biosynthesis in the bacteria, E. coli, and Lactobacillus with particular interest in acyl carrier protein.  A fluorescent analogue for CoA was first synthesized by our laboratory.  Acetyl etheno-CoA was not a substrate for citrate. Synthase.  We prepared long chain acyl etheno-CoA.  Surprisingly this analogue was shown to be about as good a detergent (measured by the critical micelle concentration) as the corresponding acyl-CoA but not nearly as inhibitory, suggesting a specific inhibitory effect that was independent of detergency.  This demonstration refuted a long-standing tenant that long chain acyl-CoA is inhibitory merely by virtue of detergency rather than specific inhibition.  Feed back inhibition of citrate synthase and, by inference, other enzymes like Acetyl CoA Carboxylase by long chain acyl CoA was now credible.

Shifting areas, we used spin labeling and electron spin resonance in collaborations beginning with sabbatical leaves with Hayes Griffith and Pat Jost at the Molecular Biology Institute at the University of Oregon (1974-75) and continuing with Derek Marsh’s laboratory at the Max-Planck-Institute for Biophysical Chemistry in Göttingen, Germany (1983-84; continued in summers until 1993), to explore specific interactions between phosphoplipids and membrane proteins.  Cardiolipin, found only in mitochondria, associates with intrinsic membrane proteins in the electron transport system, particularly cytcochrome c oxidase.  Our laboratory was the first to prepare acyl-spin labeled cardiolipin and we did it stereospecifically.  Using this analogue we showed that this lipid partitions from synthetic membrane lipid mixtures to associate with the oxidase.  The association was not specific but appeared to depend on the dual negative charges of the polar headgroup.  While the activity of the oxidase was enhanced by cardiolipin, perhaps enhancing the binding of the substrate cytochrome c, we showed that cardiolipin was not essential for activity.  Using a series of cardiolipin analogues synthesized at Clemson University containing five, four, three and two acyl chains, we showed that these analogues formed an inverted hexagonal phase, lamellar phase transitioning to inverted hexagonal phase with increasing salt, lamellar and micellar phases respectively strongly supporting the Shape Theory for phase transitions for phospholipids in general. 

Collaborating with A.G. Abbott’s laboratory, we cloned the first enzyme of polyunsaturated fatty acid biosynthesis, oleoyl-phosphatidly choline desaturase from peanut.  We demonstrated that a lesion in this enzyme was the molecular basis of high-oleate varieties of peanut.  The molecular biology of the high oleate phenotypes in these diploid plants is complex but results from MITE insertion in one allele and reduced expression of the second allele.  We expressed this enzyme in yeast.  By feeding synthetic fatty acids and electrospray mass spectroscopy to characterize the products, we examined the specificity of the enzyme.  The second double bond is always placed beta to the existing double bond and towards the methyl end suggesting that the enzyme can detect the location of a single double bond in an acyl chain.  Phosphatidyl choline seemed to be the preferred substrate, but doubly desaturated acyl chains in other classes of phospholipids was observed.

 

Grant Support

While active, my laboratory was supported by grants from the National Institute of General Medical Sciences, the National Science Foundation, the American Heart Association, the SC Heart Association, Calhoun Honors College and an institutional award to Howard Hughes Medical Institute

Awards

National Scholars Program Award of Distinction, April 18, 2007

Inducted into Clemson University Chapter of Blue Key, 2005

Resources

 

Recent Publications

Over 50 publications in leading journals in Biochemistry and in Biophysics