Studies of the Co2+-activated ribulose-1,5-bisphosphate carboxylase/oxygenase by the use of spectrophotometry.
Transient optical absorption bands are formed upon addition of ribulose-1,5-bisphosphate to the Co2+-activated ribulose-1,5-bisphosphate carboxylase/oxygenase from spinach and parsley. In the visible region, the prominent absorption band during steady state has a maximum at 610 nm. Stopped-flow technique was used to study the increase in absorbance at this wavelength, and two distinct phases in the progress curve for the approach to steady-state absorbance were observed. The rates for these two phases, respectively, were similar to those found earlier for the two enzyme-Co2+-bound intermediates using EPR technique (Brändén et al. (1987) Biochim. Biophys. Acta 916, 298-303). It is therefore proposed that most of the transient optical absorption originates from an enzyme-Co2+-coordinated ribulose-1,5-bisphosphate molecule and an enzyme-Co2+-coordinated enediolate anion of it, where bound ribulose-1,5-bisphosphate appears first. Furthermore, the most rapid phase in the progress curve is a first-order reaction, independent of the ribulose-1,5-bisphosphate concentration. This indicates that the formation of enzyme-Co2+-coordinated ribulose-1,5-bisphosphate is preceeded by another reaction in which ribulose-1,5-bisphosphate binds to the enzyme, probably without metal coordination.
Brändén
R
R
Department of Biochemistry and Biophysics, University of Göteborg, Sweden.
Janson
K
K
Nilsson
P
P
D003035:Cobalt / Q000494:pharmacology*; D004578:Electron Spin Resonance Spectroscopy; D004789:Enzyme Activation / Q000187:drug effects; D010944:Plants / Q000201:enzymology; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism*; D012274:Ribulosephosphates / Q000378:metabolism; D013057:Spectrum Analysis
D012274:Ribulosephosphates; D003035:Cobalt; D012273:Ribulose-Bisphosphate Carboxylase