[P008] Poster

1:00 PM - 1:50 PM JST(4:00 AM - 4:50 AM UTC)

[P04-578] Studies on enzymes involved in CO₂-concentrating mechanisms in brown algae

Jian-qiang Jin¹, Yuusuke Yokooji¹, Toshiyuki Shibata², ○Joseph Walker Scott¹, Haruyuki Atomi¹ (1. Kyoto University (Japan), 2. Mie University (Japan))

Keywords:

Brown algae,Carbon dioxide fixation,Enzymology

CO₂ fixation in plants, algae and cyanobacteria is carried out through ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and the Calvin-Benson-Bassham (CBB) cycle. There are also mechanisms to concentrate CO₂ in the cell, referred to as CO₂-concentrating mechanisms (CCMs), and provide CO₂ to RuBisCO. Biochemical CCMs involve enzymes such as phosphoenolpyruvate carboxylase, phosphoenolpyruvate carboxykinase, and malic enzyme. Phosphoenolpyruvate carboxylase converts CO₂ and phosphoenolpyruvate to oxaloacetate in an irreversible manner. Oxaloacetate is then converted to malate or aspartate and transported so that CO₂ is released and can be provided to RuBisCO. In conventional biochemical CCMs, phosphoenolpyruvate carboxykinase and malic enzyme are responsible for the release of CO₂. Phosphoenolpyruvate carboxykinase converts CO₂ and phosphoenolpyruvate to oxaloacetate, but the reaction is coupled ATP generation, and is thus reversible under physiological conditions. Malic enzyme catalyzes a reversible oxidative decarboxylation of malate to release CO₂ and form pyruvate while reducing NAD(P)⁺ to NAD(P)H.
Brown algae are known to exhibit rapid growth and have been suggested to harbor CCMs. However, the enzymes involved and the mechanism of concentrating CO₂ is still unclear. Here we will present our findings on the biochemical properties of enzymes potentially involved in CCM in brown algae, focusing on enzymes from organisms such as Ectocarpus siliculosus, Saccharina japonica, and Ishige okamurae.
This research was funded by the New Energy and Industrial Technology Development Organization, Grant Number JPNP18016.