The isocitrate dehydrogenase from cyanobacteria

Area of Science:

• Biochemistry
• Molecular Biology
• Microbiology

Background:

• Isocitrate dehydrogenase (ICD) is a key enzyme in cellular metabolism.
• Cyanobacteria, particularly heterocysts, possess unique metabolic pathways related to nitrogen fixation.

Purpose of the Study:

• To characterize the properties of isocitrate dehydrogenase in different cyanobacteria species.
• To investigate the regulatory mechanisms and physiological role of ICD in heterocysts versus vegetative cells.

Main Methods:

• Enzyme activity assays using crude extracts from Anacystis nidulans, Nostoc muscorum, and Anabaena cylindrica.
• Analysis of enzyme regulation by reduction charge, oxoglutarate, ATP, ADP, and thioredoxin.
• Investigating hysteretic properties and inactivation by oxidized glutathione.

Main Results:

• ICD activity is significantly higher in heterocysts than vegetative cells, and virtually absent in Anabaena cylindrica vegetative cells.
• The enzyme is negatively regulated by reduction charge and its inhibition by ATP/ADP is competitive or noncompetitive depending on the species.
• Thioredoxin activates ICD, while oxidized glutathione deactivates it, suggesting a regulatory role in cell differentiation.

Conclusions:

• The primary role of ICD in heterocysts is likely glutamate biosynthesis, not providing reducing equivalents for N2-fixation.
• ICD and thioredoxin may play a crucial role in the differentiation of cyanobacterial vegetative cells into heterocysts.