Wm Wallace Cleland, professor of biochemistry at the University of Wisconsin-Madison, passed away on March 6 of injuries sustained in an accident. He spent his last days and hours surrounded by his family.
Professor Cleland preferred to be addressed as “Mo.” He was born in Baltimore on Jan. 6, 1930, to Elizabeth and Ralph Cleland. The family moved to Bloomington, Ind., where Mo’s father became chairman of the botany department and dean of the graduate school at Indiana University.
Mo graduated from Oberlin College with a bachelor’s degree in 1950 and from the University of Wisconsin with a master’s degree in1953 and a Ph.D. in 1955. He carried out postdoctoral research under Eugene P. Kennedy at the University of Chicago and returned to the University of Wisconsin-Madison as an assistant professor in 1959. Mo advanced to professor of biochemistry in 1966. He was the Marvin J. Johnson professor of biochemistry from 1978 and the Steenbock professor of chemical sciences between 1982 and 2003.
Mo became a fellow of the American Academy of Arts and Sciences in 1977 and was elected to the National Academy of Sciences in 1985. He received the Merck Award from the American Society for Biochemistry and Molecular Biology, the Alfred Bader Award in Bioinorganic or Bioorganic Chemistry from the American Chemical Society, the Repligen Award for the Chemistry of Biological Processes from the Division of Biological Chemistry of the ACS, the Stein and Moore Award from the Protein Society and the Hilldale Award in the Physical Sciences from the University of Wisconsin-Madison. In 1978, Mo was listed among the 300 most-cited scientists.
Mo made influential contributions to enzymology throughout his career. His most widely cited work brought order into the field of multisubstrate steady-state enzyme kinetics. He published three papers on this topic in Biochimica et Biophysica Acta: “Nomenclature and rate equations,” “Inhibition: nomenclature and theory” and “Prediction of initial velocity and inhibition patterns by inspection.” In this work, Mo derived the basis for what are now known as Cleland’s rules, which allow one to write the rate equation for a multisubstrate enzyme by inspection of kinetic patterns. Mo coined the term “ping-pong kinetics” for a kinetic pattern implicating a covalently modified enzyme-substrate intermediate.
Early biochemists purified oxygen-sensitive proteins in the presence of mercaptoethanol. Problems with mercaptoethanol were its odor and that two molecules were required to reduce a disulfide. Mo studied the reducing properties of dithiol compounds analogous to dihydrolipoamide and found that dithiothreitol, also known as DTT or Cleland’s reagent, eliminated those problems. It was highly water soluble, was nearly odor-free and displayed a low reduction potential. Cleland’s reagent now can be found in most biochemical laboratories.
The enzyme-substrate binding, product-release and conformational effects intervening among the chemical steps in the action of an enzyme create a fundamental problem in mechanistic analysis. Chemists measure heavy-atom kinetic isotope effects, or KIEs, to distinguish alternative mechanisms. But binding and conformational effects in enzymes, which can limit rates, often defeat this method. In early collaborations with Wisconsin colleagues Marion O’Leary and Dexter B. Northrop, Mo set out to overcome the problems and apply KIEs to analyze chemical mechanisms in enzymatic catalysis. In the process, Mo invented the equilibrium perturbation method for measuring KIEs, especially deuterium KIEs. This method was brilliantly conceived and enabled KIEs to be measured at chemical equilibrium in a single experiment.
Mo continued with this work and became a master of enzymatic kinetic isotope effects. He neutralized the masking of chemical steps by noncovalent processes through the use of alternative substrates to increase ligand dissociation rates — through the exploitation of pH effects to find conditions at which chemical steps limit rates and through site-directed mutagenesis to make chemical steps rate-limiting. When these methods worked, KIEs on kcat (turnover rate constant) could be measured.
Mo chose the internal competition method to determine KIEs on kcat/Km. In this method, the heavy atom was a trace label at natural abundance. This method gave KIEs on kcat/Km, the second-order rate constant for reaction of an enzyme with a substrate. This was the only method available for 14C or 3H effects, because the radioactive species were always trace labels. Mo did not generally rely on radioactivity measurements. He preferred stable heavy atoms like 13C, 15N and 18O. Trace labeling with these isotopes often required chemical synthesis and always required chemical degradation of products and isotope ratio mass spectrometry. Mo never was deterred by the required chemistry. Moreover, he obtained exceedingly accurate values of the small KIEs for these isotopes. Mo was a master at dissecting complex physicochemical pathways and determining mechanisms by observing isotope-sensitive steps. He carried out multiple KIEs to refine structures of transition states and even to distinguish stepwise from concerted mechanisms.
Mo lived a full life that included being a patron of the arts. In his younger days, he enjoyed sailing and ice boating on Lake Mendota in Madison. Mo served as the commodore of the Mendota Yacht Club in 1966. He was an annual supporter of the Madison Symphony Orchestra. He was an opera lover and knew all the operas in the standard repertoire. He supported the Madison Opera and opera companies from coast to coast.
Mo was a world-class philatelist. He held many leadership positions in the United States Stamp Society, including its presidency in 1992. He published more than 300 articles in the Canal Zone Philatelist and the United States Specialist. Mo received the Hopkinson Memorial Literature Award in 1986, 2002 and 2006. He received the Smithsonian Institution’s Philatelic Achievement Award in 2008, and in 2009 the Stamp Society inducted him into the United States Stamp Society Hall of Fame.
Mo was a devoted parent, with his former wife Joan Cleland, to Elsa Cleland and Erica Shepard, and a devoted grandparent to Max, Finn and Griffin. He was exceptionally generous to colleagues worldwide, who consulted him on enzyme kinetics. He responded mercurially to requests for assistance from students, young professionals and seasoned researchers. Mo’s friends regarded him as a kind and generous adviser as well as a dominant force in enzymology.