A 160 kDa protein with carbonic anhydrase activity is complexed with rubisco on the outer surface of thylakoids

Abstract

This study provides evidence that, in the soluble fraction from buffer-washed pea thylakoids, one form of soluble carbonic anhydrase (CA) is associated with rubisco in a stromal protein complex. On native-PAGE gels, it is present as a protein band with MW approximately 160 kDa. On SDS-PAGE gels, it is resolved as a single 25-kDa polypeptide. Analysis of Western blots developed with polyclonal antibodies to barley rubisco and to soluble pea CA shows that a 160-kDa protein with CA activity is associated with rubisco in a protein complex localized on the outer surface of thylakoid membranes.

Role of Plant Carbonic Anhydrases under Stress Conditions

“…Immunocytolocalization experiments indicated that CA is a neighbor of Rubisco in the stroma of pea leaves' chloroplast [111]. One CA in the stroma of chloroplasts was later discovered to be associated with Rubisco on the outside of the thylakoid membrane [112]. In the early stages of the adaptation of sugar beet plants to a high concentration of carbon dioxide, of 700 ppm, a decrease in both the activity of the soluble and of the membranebound CAs was observed.…”

Carbonic Anhydrases in Photosynthesizing Cells of C3 Higher Plants

“…These results also appear to dismiss a proposed mechanism in which this CA takes part in increasing the local availability of СО 2 for Rubisco [43]: it had been suggested that since carboxylation of RuBP leads to two protons appearing in the medium, the equilibrium between СО 2 and bicarbonate at the site where these protons are formed should shift towards СО 2 , and the CA that is in direct contact with Rubisco accelerates this shift. However, CA and Rubisco complexes, as well as the inclusion of CA in a supramolecular protein complex consisting of Rubisco and other enzymes of the Calvin cycle have been discovered in pea and tobacco [44][45][46], serving as evidence of the above mechanism.…”

Carbonic Anhydrases in Photosynthesizing Cells of C3 Higher Plants

“…These results also appear to dismiss a proposed mechanism in which this CA takes part in increasing the local availability of CO 2 for Rubisco [43]: it had been suggested that since carboxylation of RuBP leads to two protons appearing in the medium, the equilibrium between CO 2 and bicarbonate at the site where these protons are formed should shift towards CO 2 , and the CA that is in direct contact with Rubisco accelerates this shift. However, CA and Rubisco complexes, as well as the inclusion of CA in a supramolecular protein complex consisting of Rubisco and other enzymes of the Calvin cycle have been discovered in pea and tobacco [44,45,46], serving as evidence of the above mechanism.…”