Fig. 4. Proper localization of carbonic anhydrases enhances PCCM performance.

a, Schematics of varying localization of carbonic anhydrases. The CAH3 domain starts in the centre of the intrapyrenoid tubules (radius r = 0) and the LCIB domain ends at the chloroplast envelope. Colour code as in Fig. 1d. Orange denotes region occupied by CAH3. b–e, CAH3 end radius and LCIB start radius are varied in a modelled chloroplast employing the passive CO₂ uptake strategy under air-level CO₂, with thylakoid stacks slowing inorganic carbon diffusion in the stroma (b,c) or with an impermeable starch sheath (d,e). Normalized CO₂ fixation flux (b,d) and ATP spent per CO₂ fixed (c,e) when the localizations of carbonic anhydrases are varied. f, Schematics of inorganic carbon fluxes for the localization patterns (i–iii) indicated in b–e. Colour code as in a and Fig. 1d. Dotted ticks in b–e denote pyrenoid radius as in a. Simulation parameters are the same as in Fig. 1c,d.