Only one DNA polymerase is the replication enzyme. The others participate in repair of damaged DNA, restarting stalled replication forks, or bypass 1ng damage in DNA.

TLS Online TPP Program

#Id: 7265

#Unit 6. System Physiology – Plant

TLS Online TPP Program

#Id: 7266

#Unit 6. System Physiology – Plant

Chaperonins GroEL and GroES sequester and ensure the correct folding of the newly synthesized large subunit (L). 

The assembly chaperone (RbcX)2 binds the large subunit and provides positional information for proper association of large subunit dimers to form the L8–((RbcX)2)8 complex. 

The small subunit (S) associates with L8–((RbcX)2)8, triggering a conformational change in RbcL and eliciting 

the release of (RbcX)2 and formation of the catalytically mature Rubisco holoenzyme [L]8–[S]8.

TLS Online TPP Program

#Id: 7267

#Unit 6. System Physiology – Plant

TLS Online TPP Program

#Id: 7268

#Unit 6. System Physiology – Plant

One way in which rubisco is activated involves the formation of a carbamate– Mg2+ complex on the ε-amino group of a lysine within the active site of the enzyme. Two protons are released. Activation is enhanced by the increase in Mg2+ concentration and higher pH (low H+ concentration) that result from illumination. The CO2 involved in the carbamate–Mg2+ reaction is not the same as the CO2 involved in the carboxylation of ribulose-1,5-bisphosphate.

TLS Online TPP Program

#Id: 7269

#Unit 6. System Physiology – Plant

The activity of rubisco is also regulated by light, but the enzyme itself does not respond to thioredoxin.

Two protons are released during the formation of the ternary complex rubisco–CO2–Mg2+, so activation is promoted by an increase in both pH and Mg2+ concentration.

TLS Online TPP Program

#Id: 7270

#Unit 6. System Physiology – Plant

The binding of sugar phosphates, such as ribulose-1,5-bisphosphate, to rubisco prevents carbamylation. The sugar phosphates can be removed by the enzyme rubisco activase, in a reaction that requires ATP. The primary role of rubisco activase is to accelerate the release of bound sugar phosphates, thus preparing rubisco for carbamylation