, Volume 87, Issue 2, pp 195-204
Date: 23 Jan 2006

Kinetic Analysis of the Slow Inactivation of Rubisco During Catalysis: Effects of Temperature, O2 and Mg++

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Abstract

The effect of temperature, O2 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 °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 CO2 increased the extent of fallover but only caused a marginal increase in fallover rate in agreement with results reported previously. In contrast, increased O2 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 CO2 or Mg++, and high O2. The physiological importance of these factors in affecting Rubisco fallover and contributing to photosynthetic inhibition at high temperatures in planta are discussed.

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