Potent Inhibition of Ribulose-Bisphosphate Carboxylase by an Oxidized Impurity in Ribulose-1,5-Bisphosphate1

Oxidation of d-ribulose-1,5-bisphosphate (ribulose-P2) during synthesis and/or storage produces d-glycero-2,3-pentodiulose-1,5-bisphosphate (pentodiulose-P2), a potent slow, tight-binding inhibitor of spinach (Spinacia oleracea L.) ribulose-P2 carboxylase/oxygenase (Rubisco). Differing degrees of contamination with pentodiulose-P2 caused the decline in Rubisco activity seen during Rubisco assay time courses to vary between different preparations of ribulose-P2. With some ribulose-P2 preparations, this compound can be the dominant cause of the decline, far exceeding the significance of the catalytic by-product, d-xylulose-1,5-bisphosphate. Unlike xylulose-1,5-bisphosphate, pentodiulose-P2 did not appear to be a significant by-product of catalysis by wild-type Rubisco at saturating CO2 concentration. It was produced slowly during frozen storage of ribulose-P2, even at low pH, more rapidly in Rubisco assay buffers at room temperature, and particularly rapidly on deliberate oxidation of ribulose-P2 with Cu2+. Its formation was prevented by the exclusion of transition metals and O2. Pentodiulose-P2 was unstable and decayed to a variety of other less-inhibitory compounds, particularly in the presence of some buffers. However, it formed a tight, stable complex with carbamylated spinach Rubisco, which could be isolated by gel filtration, presumably because its structure mimics that of the enediol intermediate of Rubisco catalysis. Rubisco catalyzes the cleavage of pentodiulose-P2 by H2O2, producing P-glycolate.

University of Michigan Men's Basketball Team, 2004

Back Row: coach Tommy Amaker, director of basketball operations Kirsten Green, asst. coach Chuck Swenson, asst. coach Charles E. Ramsey, Lester Abram, Brent Petway, Amadou Ba, Chris Hunter, Courtney Sims, Graham Brown, John Andrews, asst. coach Andrew Moore, strength coach Jim Plocki, academic advisor Support Angie Heath, equip. mngr. Bob Bland.

Front Row: trainer Eric Broekhuizen, mngr. Michael Oh, Sherrod Harrell, Daniel Horton, Colin Dill, Bernard Robinson Jr., J.C. Mathis, Dion Harris, Dani Wohl, Manager Matt Duprey, admin. asst. Lucien St. Gerard.

University of Michigan Men's Basketball Team, 2004

Back Row: Lester Abram, Brent Petway, Amadou Ba, Chris Hunter, Courtney Sims, Graham Brown, and John Andrews.

Front Row: Sherrod Harrell, Daniel Horton, Colin Dill, Bernard Robinson Jr., J.C. Mathis, Dion Harris, and Dani Wohl.

University of Michigan Men's Basketball Team, 2004 NIT Champions

Back Row: Colin Dill, Brett Petway, Chris Hunter, Courtney Sims, Amadou Ba, Graham Brown, J.C. Mathis

Front Row:Dani Wohl, Daniel Horton, Sherrod Harrell, Lester Abram, John Andrews, Dion Harris, Ashtyn Bell

University of Michigan Men's Basketball Team, 2005

Back Row: head coach Tommy Amaker, director of basketball operations Kirsten Green, asst. coach Chuck Swenson, asst. coach Charles Ramsey, John Andrews, Brent Petway, Courtney Sims, Chris Hunter, Amadou Ba, Graham Brown, Ronald Coleman, asst. coach Andrew More academic advisor Angie Beck, strength coach Jim Plocki, equip. mngr. Bob Bland.

Front Row: administrative asst. Lucien St. Gerard, Dani Wohl, Dion Harris, Sherrod Harrell, J.C. Mathis, Lester Abram, Daniel Bell, sr. mngr. Matt Duprey.