Abstract
Ribulose‐1,5‐bisphosphate carboxylase/oxygenase is the key enzyme for photosynthesis. The wild‐type and mutant (amino‐acid substitutions in the catalytically important loop 6 region) enzymes from Chlamydomonas reinhardtii, a unicellular green alga, were crystallized. Wild‐type, single‐mutant (V331A) and two double‐mutant (V331A/T342I and V331A/G344S) proteins were activated with cofactors CO2 and Mg2+, complexed with the substrate analog 2′‐carboxyarabinitol‐1,5‐bisphosphate, and crystallized in apparently isomorphous forms. Unit‐cell determinations have been completed for three of the enzymes. They display orthorhombic symmetry with similar cell parameters: wild type a = 130.4, b = 203.3, c = 208.5 Å; single mutant (V331A) a = 128.0, b = 203.0, c = 207.0Å; and double mutant (V331A/T342I) a = 130.0, b = 202.1, c = 209.7 Å. Crystals of the wild‐type and single‐mutant (V331A) enzymes diffracted to 2.8 Å. A small crystal of the double‐mutant (V331A/T342I) enzyme diffracted to 6 Å. A partial data set (68% complete) of the wild‐type protein has been collected at room temperature to about 3.5 Å.