Culinary Chemist, Kathryn Perez, moves from the kitchen to the chemistry lab

Culinary chemist

2009 Amgen Scholar moves from the kitchen to the chemistry lab

Several years before her summer with the Amgen Scholars in 2009, Kathryn Pérez was starting a career in culinary arts. As a student, she immersed herself in classes on cooking, developing menus and setting prices, and later she put those skills to practice in several Miami restaurants. But she always longed to go back to school and learn the science behind the smells, textures and tastes she was creating.

Little did she know at the time that her studies would take her far beyond food and into the chemistry and kinetics of molecules. In 2007, at 27 she decided to begin a degree in nutrition at Florida International University in Miami. Most classes were focused on nutritional counseling, but after taking several introductory chemistry classes, she made it her major. "I started seeing how chemistry relates to almost everything you do and I really enjoyed it," she says. She was hooked.

After a stint doing tissue culture in a breast cancer lab, Pérez started working in Jaroslava Miksovska's lab on biophysical chemistry, studying the thermodynamics and kinetics of proteins. Additional classes, and reading books from Hervé This—a French physical chemist and molecular gastronomist who discovered the perfect temperature at which to cook an egg—inspired and solidified her interest in physical chemistry.

Fixing nitrogen

Pérez wanted to pursue her interest in chemistry further through a summer research program. When she decided to apply to the Amgen Scholars Program at Caltech, she got in touch with physical chemist Mitchio Okumura at the suggestion of one of her professors. She and Okumura talked about potential projects in atmospheric chemical reactions.

Okumura got back to her with an idea he and his colleague Doug Rees had been discussing for years: how some bacteria are able to convert nitrogen gas (N2) in the atmosphere to ammonia or NH3. In fact, it's a question that scientists had been trying to understand for half a century.

All living things need nitrogen—it helps form the backbone of proteins and the building blocks of DNA—but humans can't directly convert, or fix, nitrogen gas into a form that useful in metabolism because of its sturdy triple bond. In the early 1900s, Fritz Haber and Carl Bosch worked out a method that uses high temperature and high pressure to break the bonds in vitro, under conditions that are much harsher than those required for nitrogen-fixing bacteria.

Rees started working with a bacterium, Azotobacter vinelandii, which converts nitrogen gas under normal temperatures and pressure, hoping to find the secret to its abilities. His group determined the precise molecular structure of the main enzyme involved in fixation, called nitrogenase, but still lacked sufficient knowledge of the chemical process involved in the conversion.

Rees and Okumura hypothesized that nitrogenase works by generating an excited state of nitrogen, pushing the nitrogen atoms farther apart and making their bonds easier to break. If that was true, the nitrogen might give off light when it returned to the resting state, much like what happens during a lightning storm.

Culture container

"Kathryn was fearless and enthusiastic," Rees says. She built an instrument that detected light emission from a culture of nitrogen-fixing bacteria. The key component was a photomultiplier tube, which measures light in photons, attached to the growing culture of bacteria. Pérez wired the electronics to detect photons over time.

"I have always enjoyed building things, but I'm not engineer," says Pérez. It took 10 weeks to get to the key experiment, a comparison between the amount of photons emitted from a culture of bacteria exposed to nitrogen gas and one exposed to a mix of control gasses: oxygen and argon. Although the nitrogen gas culture emitted more photons, the group has to do additional control experiments to be sure that the result could be attributed to nitrogenase activity and not a difference in culture conditions. Still, "we were pretty excited," Rees says. "Kathryn really got things off to a great start."

Pérez says her experience with the Amgen Scholars solidified her plan to continue physical chemistry work with biological applications. "Caltech has such amazing resources," she says. "I really got to see what it was like to develop a project and work out various problems along the way." With the help of graduate student Kana Takematsu, Pérez was able to navigate easily between two labs—armed with vastly different backgrounds and techniques—to build the culture container.

In fact, Pérez hopes to build on the nitrogenase project as a PhD student. Her future research questions, she adds, will require the same sort of creative problem-solving as that fostered in the kitchen.

As a 2009 Amgen Scholar, Kathryn Pérez performed her summer research in Mitchio Okumura's and Doug Rees's laboratories at California Institute of Technology in Pasadena. She is in her third year of study in chemistry at Florida International University in Miami. She plans to pursue a PhD in physical chemistry.