Paving the path

Abstract

The Path of Carbon in Photosynthesis evolved in the minds of Sam Ruben and Martin Kamen as they followed incorporation of radioactive 11CO2 in their many experiments, 1938 to 1942. With the concepts and collaboration of C. B. van Niel it became clear that reduction of CO2 can occur in the dark and may require processes similar to bacterial systems. It could not involve the century-old A. von Baeyer theory's photochemical reduction of CO2 adsorbed on chlorophyll which had guided decades of painstaking efforts, of R. Willstätter and A. Stoll and many others, in vain searches for formaldehyde. In 1942 Sam Ruben gave me all of his home-made 14CO2 to look for the first steps of the path of carbon in photosynthesis. Measurements were tedious and activities low but progress was real. Liquid-liquid partition of the radioactivity indicated chemical properties of the products and their derivatives. Interrupted by the war and Sam Ruben¿s tragic accidental death, I accepted Melvin Calvin's invitation to continue The Path and we established our lab in the Old Radiation Laboratory next to Ernest Lawrence's cyclotron. Pre-illuminated algae rapidly reduced 14CO2 in the dark! Simple 'partition'-based separations on paper chromatograms extended the earlier methodology. Sedoheptulose and ribulose made surprise appearances. Soon it became clear that Nature had selected ribulose bisphosphate as its universal CO2 acceptor molecule. Finally, our isolation of carboxydismutase in 1954 revealed its identity with Sam Wildman's Fraction 1 protein. The Path was paved with one of this planet's major proteins!