Why Does Life Need Water?

Masayoshi Nakasako (Associate Professor, Department of Physics)

Do you remember this spring, when two satellites arrived on Mars and roamed its desert-like surface in search of traces of life? I watched the news thinking they were trying to find fossils or tracks of crawling creatures, but it seemed what they were actually looking for were compounds, eroded rocks, or geological strata that could prove water once existed on Mars. As this example shows, many scientists, including those in NASA's Mars exploration project, seem to operate on the logic that "the presence of water" equals "the origin of life." However, it seems to me that no one has been able to scientifically substantiate this logic.

In our laboratory, we are searching for answers to a very fundamental question: just how important is the liquid we call "water," whose benefits we enjoy as a matter of course, for life activities, and what kind of influence does it have? It has already been seven years since we began our research to explore the relationship between life and water at the molecular and atomic levels, and now we can explain, just a little, the importance of water. To investigate in detail at the atomic and molecular scale how proteins and nucleic acids—the components of living organisms and the agents of life phenomena—interact with water (Fig. 1), we conduct research using X-rays (Figs. 2 and 3) and neutrons obtained from a particle accelerator.

If you gaze intently at a glass of water and drink it while savoring it carefully, you might be able to imagine many things about the relationship between water and life.

Fig. 1: If you could magnify the area around a cell by about 100 million times, you would see proteins (ribbon diagram) moving in water, depicted as blue spheres. The thickness of the cell membrane is four nanometers (one-billionth of a meter).

Fig. 2: This is an electron accelerator called SPring-8, located in the Nishi-Harima region of Hyogo Prefecture. Our laboratory conducts experiments using X-rays at this facility about five times a year. The white, belt-like structure surrounding the central mountain is the building called the storage ring, which has a circumference of 1.5 km.

Fig. 3: Inside the building shown in the photo in Fig. 2, there are about 70 large experimental apparatuses. This is a photo taken during an experiment on one of them. We operate various complex devices and conduct experiments all night long.