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Title: KINETIC ANALYSIS OF THE SLOW INACTIVATION OF RUBISCO DURING CATALYSIS: EFFECT OF TEMPERATURE, O2 AND MG++.

Author
item KIM, KANGMIN
item PORTIS JR, ARCHIE

Submitted to: Photosynthesis Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/2/2005
Publication Date: N/A
Citation: N/A

Interpretive Summary: The activity of Rubisco, the enzyme that captures carbon dioxide, often limits photosynthesis, the process by which plants use light energy from the sun to make carbohydrates for growth from carbon dioxide and water. The activity of Ribisco is known to decline with time due to the formation of aberrant products by various side reactions. In this study we characterized the kinetics of the fallover process under various conditions that encompass those occurring in vivo. Our analysis of the influence of the parameters examined on the kinetics provides new insights into the importance of fallover in reducing the activity of Rubisco in the absence sufficient activity of its helper protein, activase. This information will benefit scientists attempting to modify the properties of Rubisco and activase in ways beneficial for increased photosynthesis by crop plants.

Technical Abstract: The effect of temperature, 02 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 degree 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 increaed the fallover of Rubsico 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 and 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.