scholarly journals Studies on the assembly of large subunits of ribulose bisphosphate carboxylase in isolated pea chloroplasts.

1982 ◽  
Vol 94 (1) ◽  
pp. 20-27 ◽  
Author(s):  
H Roy ◽  
M Bloom ◽  
P Milos ◽  
M Monroe
Keyword(s):  
Large Subunit ◽  
Ribulose Bisphosphate Carboxylase ◽  
Ribulose Bisphosphate ◽  
Dissociation Reaction ◽  
Bisphosphate Carboxylase ◽  
In Organello ◽  
Intact Chloroplasts ◽  
Isolated Chloroplasts

Ribulose bisphosphate carboxylase consists of cytoplasmically synthesized "small" subunits and chloroplast-synthesized "large" subunits. Large subunits of ribulose bisphosphate carboxylase synthesized in vivo or in organello can be recovered from intact chloroplasts in the form of two different complexes with sedimentation coefficients of 7S and 29S. About one-third to one-half of the large subunits synthesized in isolated chloroplasts are found in the 7S complex, the remainder being found in the 29S complex. Upon prolonged illumination of the chloroplasts, newly synthesized large subunits accumulate in the 18S ribulose bisphosphate carboxylase molecule and disappear from both the 7S and the 29S large subunit complexes. The 29S complex undergoes an in vitro dissociation reaction and is not as stable as ribulose bisphosphate carboxylase. The data indicate that (a) the 7S large subunit complex is a chloroplast product, the (b) the 29S large subunit complex is labeled in vivo, that (c) each of these two complexes can account quantitatively for all the large subunits assembled into RuBPCase in organello, and that (d) excess large subunits are degraded in chloroplasts.

scholarly journals Inhibition of ribulose bisphosphate carboxylase assembly by antibody to a binding protein.

1986 ◽  
Vol 103 (4) ◽  
pp. 1327-1335 ◽  
Author(s):  
S Cannon ◽  
P Wang ◽  
H Roy
Keyword(s):  
Higher Plants ◽  
Binding Protein ◽  
Large Subunit ◽  
Ribulose Bisphosphate Carboxylase ◽  
Ribulose Bisphosphate ◽  
Dual Effect ◽  
Bisphosphate Carboxylase ◽  
Low Concentrations ◽  
The One

We have developed an assay to monitor in vitro the posttranslational assembly of the chloroplast protein, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO). Most of the newly synthesized 55-kD catalytic ("large") subunits of this enzyme occur in a 29S complex together with 60- and 61-kD "binding" proteins. When the 29S complex is incubated with ATP and MgCl2 it dissociates into subunits, and the formerly bound large subunits now sediment at 7S (still faster than expected for a monomer). Upon incubation at 24 degrees C, these large subunits assemble into RuBisCO. The minority of newly made large subunits which are not bound to the 29S complex also sediment at 7S. When endogenous ATP was removed by addition of hexokinase and glucose, the dissociation of the 29S complex was inhibited. Nevertheless, the 7S large subunits assembled into RuBisCO, and did so to a greater extent than in controls retaining endogenous ATP. Thus the 7S large subunits are also assembly competent, at least when ATP is removed. Apparently, in chloroplast extracts, ATP can have a dual effect on the assembly of RuBisCO: on the one hand, even at low concentrations it can inhibit incorporation of 7S large subunits RuBisCO; on the other hand, at higher concentrations it can lead to substantial buildup of the 7S large subunit pool by causing dissociation of the 29S complex, and stimulate overall assembly. At both high and zero concentrations of ATP, however, antibody to the binding protein inhibited the assembly of endogenous large subunits into RuBisCO. Thus it appears that all assembly-competent large subunits are associated with the binding protein, either in the 7S complex or in the 29S complex. The involvement of the binding protein in RuBisCO assembly may represent the first example of non-autonomous protein assembly in higher plants and may pose problems for the genetic engineering of RuBisCO from these organisms.

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