HEAT DENATURATION PROFILES OF RUBISCO AND RUBISCO ACTIVASE AND THE INABILITY OF RUBISCO ACTIVASE TO RESTORE ACTIVITY OF HEAT-DENATURED RUBISCO

Authors: ECKARDT, NANCY - PLANT BIOLOGY UOFI URBANA; PORTIS JR, ARCHIE

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/11/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: The activity of Rubisco, the enzyme that captures carbon dioxide, is reported to be inhibited by short term exposures to moderate temperatures which reduce 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 Rubisco is determined and hence regulated by another enzyme known as Rubisco activase. Rubisco activase was recently reported to restore activity to Rubisco which had been partially inactivated by heat treatment of the isolated protein, an activity not previously observed. In this study we found that isolated Rubisco was actually much more stable to heat than Rubisco activase and that neither seemed to alter or reverse the effects of heat treatment on the other. This information will benefit scientists attempting to modify the properties and regulation of Rubisco in ways beneficial for protection of crop plants from the detrimental effects of heat.

Technical Abstract: We compared the heat-denaturation profiles of Rubisco and Rubisco activase and further examined the ability of Rubisco activase to restore activity of heat-denatured Rubisco originally reported by Sanchez de Jimenez et al. (1995, Biochem 34:2826-2831). Rubisco was heat-treated in both the carbamylated and uncarbamylated form and in the presence and absence of 10 mM DTT. Both forms were highly resistant to heat denaturation and further protection was gained in the presence of DTT. A 50 percent loss in total activity occurred after 1 h at 57.5 and 55.2 degree for uncarbamylated Rubisco, and at 60.2 and 59.6 degree for carbamylated Rubisco, in each case with and without DTT, respectively. In contrast, Rubisco activase lost 50 percent activity after only 5 min at 33 degree C and the loss in activity was not affected by the presence of Rubisco. When Rubisco, heat denatured to various extents, was incubated at room temperature with Rubisco activase or BSA as a control, Rubisco activase did not have a significant specific ability to restore Rubisco activity. We conclude that Rubisco activase alone: (a) does not have the ability to restore the activity of heat-denatured Rubisco; and (b) is unlikely to protect or restore Rubisco activity from heat denaturation in vivo because it is more heat labile than Rubisco.