Editing Chloroplast (section)

==== RuBisCO ====
{{main|RuBisCO}}
{{plain image with caption|File:Rubisco.png|'''RuBisCO''', shown here in a [[space-filling model]], is the main enzyme responsible for [[carbon fixation]] in chloroplasts.|300px|right|top|triangle|#aaa}}

The chloroplast stroma contains many proteins, though the most common and important is [[RuBisCO]], which is probably also the most abundant protein on the planet.<ref name="Campbell-2009b" /> [[RuBisCO]] is the enzyme that fixes [[CO2|CO{{sub|2}}]] into sugar molecules. In [[C3 plant|{{C3}} plants]], RuBisCO is abundant in all chloroplasts, though in [[C4 plant|{{C4}} plants]], it is confined to the [[bundle sheath]] chloroplasts, where the [[Calvin cycle]] is carried out in {{C4}} plants.<ref name="Gunning-1996a" />