David B. Knaff Paul Whitfield Horn Professor Co-Director, TTU Center for Biotechnology and Genomics Ph.D., Yale University, 1966 Postdoctoral Study, University of California, Berkeley, 1966-1968 Phone: (806) 742-0288 Fax: (806) 742-1289

Biochemistry

• Photosynthesis
• Biological Electron Transfer
• Iron-Containing Proteins
• Plant Nitrogen and Sulfur Metabolism
• Disulfide-Containing Regulatory Proteins
  

The iron-sulfur protein ferredoxin plays a key role in photosynthesis in all oxygen-evolving organisms. Ferredoxin, which contains a single [2Fe-2S] cluster that functions as a low-potential, one-electron carrier, is reduced in a light-dependent reaction and subsequently serves as the electron donor for a large number of electron-requiring processes.  Prof. Knaff’s group studies five enzymes that use reduced ferredoxin as the electron donor: sulfite reductase; nitrate reductase; nitrite reductase; thioredoxin reductase; and glutamate synthase. A major focus of this work is identification of the specific protein domains involved in the interactions between ferredoxin and these enzymes. Kinetic and spectroscopic measurements are also being carried out to elucidate the mechanisms of several of these enzymes and x-ray crystallography is  being used to determine three-dimensional structures for nitrite reductase and glutamate synthase.

A key step in sulfate assimilation involves the reduction of 5’-adenylsulfate (APS), a reaction catalyzed by the enzyme APS reductase.  Prof. Knaff’s group is studying the mechanism of APS reductases, isolated from bacteria, algae and plants, with particular emphasis on the roles of disulfide/dithiol redox couples and of a unique [4Fe-4S] cluster in the enzyme mechanism.  X-ray crystallography and NMR spectroscopy are being used in attempts to determine the structures of these enzymes.  A possible role for APS reductase in the response of plants to oxidative stress is also being explored.

Thioredoxins and glutaredoxins are small ubiquitous proteins that contain a single disulfide in the oxidized form, which is converted to two thiols in the reduced form.  Prof. Knaff’s group is studying the role of these proteins in the regulation of enzymatic activity and of gene expression and their role in protecting cells against oxidative damage.  Studies of the mechanism of disulfide reduction are also being carried out.