During the early part of the twentieth century, women were rarely able to find a career related to chemistry. However, there were three particular fields that were havens for women: crystallography (to which physicist Dorothy Hodgkin contributed); radioactivity (a field that physicist Lise Meitner and chemist Marie Curie excelled in); and biochemistry, where Mary Caldwell was able to pursue a lifelong career.
Caldwell was born in 1890 in Bogota, Colombia, to American parents. Her parents strongly supported the concept of higher education, and all five children in her immediate family became scholars or educators. In the United States, women's colleges were a major avenue for young women to obtain a degree, and Caldwell attended Western College for Women in Oxford, Ohio. She received a B.S. in 1913 and was hired by the same institution as an instructor the following year. In 1917 she was promoted to the rank of assistant professor. Caldwell remained only one more year at Western College, deciding that she needed to acquire more specialized knowledge if she was going to follow her dreams.
In 1918 Caldwell entered Columbia University, in New York, from which she received an M.S. in 1919 and a Ph.D. in 1921. Caldwell was so talented that she was immediately hired by Columbia as an instructor. The only woman in a department at a time when the very idea of women serving as chemistry faculty was almost totally unheard of beyond women's colleges, she rose through the ranks to full professorship in 1948.
Besides carrying a heavy teaching load, Caldwell developed a strong research program in nutrition and biochemistry. Her particular interest was the amylase family of enzymes. Enzymes dramatically speed up the rate at which chemical reactions occur in biological systems. Without enzymes, the complex human body would be unable to function. The amylase enzymes are those that break down starch into sugars; Caldwell's specific interest was pancreatic amylase, the version of the enzyme present in the mammalian pancreas. When she started her research, she was dissatisfied with the purity of the then commercially available enzyme. Over the next two decades she developed methods for producing pure crystalline amylase. Today, purified amylases are used in industry for fermentation, for wallpaper sizing, and in preprepared foods.
The methods Caldwell developed were applicable to other enzymes, and they were used by laboratories in the United States and Europe as a general enzyme purification procedure. Having isolated the pure enzyme, subsequent research in her laboratory showed for the first time that amylases were proteins.
Caldwell served as an important role model for aspiring women chemists. At a time when there were very few women chemists, she encouraged her women students to further pursue their education and research and become chemists and biochemists themselves. She retired in 1959, and the following year she was awarded the Garvan Medal by the American Chemical Society. This medal was awarded to a woman chemist for outstanding achievement, and for Caldwell, receiving the medal was the high point of her life. Outside of her work, she was an avid hiker until a muscular disease afflicted her. She died in Fishkill, New York, in 1972.
Geoffrey W. Rayner-Canham
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