Bettie Sue Siler Masters is an adjunct professor at Duke University known for her work on nitric oxide synthase and cytochrome P450 reductase.

[3] In 1990, she moved to the University of Texas Health Science Center at San Antonio where she was named as the Robert A. Welch Distinguished Professor in Chemistry.

[6][7] She went on to develop methods to purify enzymes, such as cytochrome P450 reductase, which allows investigation into their biochemical properties[8] and identification of the active sites of the protein through x-ray crystallography.

[9] Concerning nitric oxide synthase, she examined the atomic structure of the endothelial isoenzyme, the zinc bound within the protein, and the co-factors required (heme and tetrahydrobiopterin).

[3] In 1990, Masters was recruited to the University of Texas Health Science Center at San Antonio as the first Robert A. Welch Distinguished Professor in Chemistry.