Kinetic analysis of the slow inactivation of Rubisco during catalysis: effects of temperature, O2 and Mg(++).

The effect of temperature, O(2) and Mg(++) on the kinetic characteristics of the slow inactivation (fallover) of Rubisco isolated from spinach (Spinacia oleracea L.) was determined. Comparing 25 and 45 degrees C, the rate of activity decline of Rubisco increased by 20-fold, but the final ratio of steady state to initial activity increased from 0.38 to 0.62, respectively. Low CO(2) increased the extent of fallover but only caused a marginal increase in fallover rate in agreement with results reported previously. In contrast, increased O(2) during catalysis significantly increased only the fallover rate. Low Mg(++) greatly increased the fallover of Rubisco both in rate and extent. Rubisco carbamylation was assayed using a new separation technique and it revealed that a loss of carbamylation largely accounted for the increased fallover observed with low Mg(++). In conclusion, Rubisco fallover is facilitated by high temperature, low concentration of CO(2) or Mg(++), and high O(2). The physiological importance of these factors in affecting Rubisco fallover and contributing to photosynthetic inhibition at high temperatures in planta are discussed.