Ken Sauer: 56 years of research, and counting

  • Photosystems I and II are located near one another in a thylakoid membrane internal to the chloroplast—a greencolored organelle visible in the cells of plants and algae.
  • PS II provides the water-splitting capability, which requires promoting four electrons using four absorbed photons to form and release O2 from two water molecules and transferring four electrons to PS I.
  • Following the absorption of more photons to provide the necessary energy, PS I is able to transfer electrons to ribulose bis-phosphate carboxylase (Rubisco), thereby reducing CO2 ultimately to sugar and other carbohydrates. It was the accomplishment of unraveling the mechanism of this process that won the Nobel Prize for Calvin and his associates.

In 1960 Ken Sauer came to UC Berkeley as a postdoc in the lab of Melvin Calvin. One year after Sauer’s arrival, Calvin received the 1961 Nobel Prize in Chemistry for his application of carbon-14 to his research on carbon dioxide assimilation in plants.

Sauer retired in 2001, 41 years and 240 papers later. He has continued to publish in retirement and, at age 84, remains active in the College of Chemistry and at LBNL. Sauer is the bridge between the current generation of photosynthesis researchers at UC Berkeley and the heyday of the Calvin research group.

Sauer was born in Cleveland, OH, in 1931 and graduated from Oberlin College in 1953 with an A.B. in chemistry. That fall he moved to Cambridge, MA, to attend Harvard. His research mentor, George Kistiakowsky, had left Russia and immigrated to the United States in 1926.

Kistiakowsky was an explosives expert for the Manhattan Project in WWII. After the war he returned to the Harvard faculty and subsequently served as President Eisenhower’s science adviser. His daughter, Vera Kistiakowsky, is a physicist who earned her Ph.D. at Berkeley in 1952.

“At Harvard I made use of a technique called flash photolysis. During WWII powerful flashlamp sources were developed for military airborne photography, and many big capacitors became available as surplus items after the war. We used flash photolysis to study chemical dynamics initiated by brief, but intense, bursts of light, in much the same way as pulsed lasers are used today.”

In 1957, the year before his Ph.D. was awarded, Sauer accepted a position teaching at the American University of Beirut, Lebanon. Says Sauer, “The founding of American University had occurred in 1860—even before that of UC Berkeley. In the late 1950s, Beirut was an amazing place to teach. It was the financial center of the Middle East, with 10,000 Americans living there.

“I met my wife Margie in Beirut while she was teaching in the American Community School. We met while singing, appropriately, in a performance of Amahl and the Night Visitors. We have continued to sing together in Bay Area choral groups to this day. From Beirut we travelled all over the region, often by motor scooter. Our oldest son, the first of our four boys, was born there.

“Although Lebanon was hard to leave, after three years I thought that it was time to return to the United States. Colleagues described Berkeley as the Beirut of the west coast of the U.S., so I applied and was offered a postdoctoral opportunity working with Melvin Calvin. “By the time I arrived, most of Calvin’s Nobel Prize-winning research had already been conducted. He had assembled a large group of grad students and postdocs during the 1950s to attempt to use carbon-14, which was first synthesized at LBNL in 1940, to understand the chemical pathways used by plants to conduct photosynthesis and assimilate carbon dioxide from the atmosphere.”

Thousands of experiments were run—many making use of paper chromatography to separate and determine the identities of intermediates and products—before the nature of the carbon cycle in algae was revealed. The result was known as the Calvin cycle, although scientists often refer to it as the Calvin-Benson-Bassham cycle, in honor of Andrew Benson (B.S. ’39, Chem) and James “Al” Bassham (B.S. ’45, Ph.D. ’49, Chem), who co-discovered the cycle along with Calvin.

As a postdoc, Sauer co-authored his first article with Calvin in 1962. His early studies, carried out in collaboration with Roderic Park in Berkeley’s botany department, involved pioneering research on the electro-optical spectroscopic properties of photosynthetic pigmented membranes from spinach chloroplasts.

In 1963 Sauer received an unsolicited offer to become a faculty member of the botany department. When Calvin got wind of this, he urged his colleagues to make a counter-offer of an assistant professorship in the chemistry department, which Sauer accepted. Comments Sauer, “The decision was actually easy to make. I knew very little about botany. I was
trained as a physical chemist.”

Portrait of Ken Sauer.

After his faculty appointment Sauer worked with Ignacio Tinoco and James Wang to initiate a course in physical chemistry for biology scientists—first designated Chem 109 and subsequently listed as Chem 130. Sauer notes, “A Berkeley colleague, Bruce Mahan, had also been a student of Kistiakowsky, and for a time we both lived in the same group house at Harvard. It was Mahan who started the Chem 4 course at Berkeley, which became a model for similar courses at universities all across the country.”

After the death of Mahan in 1982, Sauer inherited Chem 4 and continued teaching it until his retirement in 2001. He has served as an adviser or member of selection committees for the France-Berkeley Fund, the Study Abroad program and the Haas Scholars program.

By the time Sauer first came to Berkeley in 1960, photosynthesis was known to involve two light reactions, each acting in a chlorophyllcontaining protein complex designated Photosystem I (PS I) and Photosystem II (PS II). The two photosystems, along with the electron transport chain that connects them, are known as the Z-scheme. feature

The Z-scheme was recognized conceptually at the time, but was not understood at the molecular level. During his three postdoctoral years in Calvin’s chemical biodynamics research group, Sauer began to explore these photosynthetic light reactions, and he later spent most of his career exploring the mysteries of the Z-scheme.

For the last four decades Sauer has focused on a manganese-calciumoxygen cluster, known as the oxygen-evolving complex, located in Photosystem II of plants, algae and cyanobacteria. He has developed sophisticated analytical devices to provide a more detailed picture of the nature of the components and their arrangement in the photosynthetic light reactions.

Sauer and his colleagues have been able to use advances in X-ray absorption spectrometry (XAS), a method that is particularly valuable for investigating the environment and involvement of metal atoms in biomolecules. Access to facilities like the Advanced Light Source at LBNL is invaluable to his research on studying metal centers in complicated redox-active metalloenzymes like PS II.

In the 1980s and 1990s Sauer teamed up with LBNL colleagues Melvin Klein and Vittal Yachandra in research that led to more than 20 papers. The threesome narrowed the range of possible structures and oxidation-state changes that were cycled in PS II to produce oxygen molecules and energetic electrons.

Klein died in 2000, and Sauer and Yachandra continued publishing with a younger colleague, Junko Yano, for another decade. The picture has steadily gotten clearer, but some significant details of the structure and function of PS II remain unresolved, and the research continues to this day.

Now 15 years into retirement, Sauer is taking a more macroscopic view of photosynthesis and how it may have evolved. The O2-producing complex probably was functioning some time before the halfway point of Earth’s 4.6-billion-year existence and has been largely conserved ever since.

“It’s fascinating to me that there’s been no significant change in more than 2.5 billion years,” says Sauer. “Simple photosynthetic bacteria in the ocean and much more diverse land plants use essentially the same oxygen-evolving complex. How did it arise, and why has it continued essentially unchanged for so long?” Sauer has studied manganese-oxide minerals using XAS and noted that many exhibit surface sites that are analogous to the photosynthetic water-oxidation complex. Says Sauer, “Primitive photosynthetic bacteria could have adapted the potentially active sites in the rocks to help oxidize water and use the bacterial genetically encoded proteins to surround and assemble this important photo-catalytic complex.” Ever curious, Sauer is excited about the dramatic increase in genomic information that is allowing researchers to trace the evolution of the huge variety of photosynthetic organisms during the last three billion years of life on Earth. He is happy to note the ongoing research of Graham Fleming, Naomi Ginsberg and David Savage in the college, along with that of other campus and LBNL researchers.

With continuing encouragement from Sauer, the Berkeley tradition of photosynthesis research is alive and well, and constantly evolving.