Hydrogenase activities in cyanobacteria

Area of Science:

• Biochemistry
• Microbiology
• Photosynthesis

Background:

• Hydrogenases are crucial enzymes in microbial metabolism, involved in hydrogen production and consumption.
• Cyanobacteria possess hydrogenase activity, but the diversity and regulation of these enzymes are not fully understood.

Purpose of the Study:

• To investigate the role of nickel in hydrogenase expression and activity in Anacystis nidulans.
• To characterize and differentiate hydrogenase fractions in the cyanobacterium Anabaena 7119.
• To explore the influence of environmental conditions and regulatory molecules on hydrogenase function.

Main Methods:

• Enzyme assays for hydrogen uptake and evolution using specific electron acceptors and donors.
• Enzyme purification using ion-exchange chromatography (DE-52 cellulose).
• Inhibition studies using heavy metals and sulfhydryl-reactive reagents.

Main Results:

• Nickel (Ni) is required for both hydrogen uptake and evolution in Anacystis nidulans.
• Hydrogenase activity in Anacystis and Anabaena extracts is inhibited by Cu2+, p-chloromercuribenzoate, and HgCl2, indicating the involvement of sulfhydryl groups.
• Two distinct hydrogenase fractions were isolated from Anabaena 7119: an "uptake" hydrogenase and a "reversible" hydrogenase.
• The "reversible" hydrogenase activity was enhanced under anaerobic conditions, while the "uptake" hydrogenase was activated by reduced thioredoxin.

Conclusions:

• Nickel is essential for hydrogenase expression and function in cyanobacteria.
• Cyanobacteria possess multiple hydrogenase types with distinct catalytic and regulatory properties.
• Thioredoxin may play a role in regulating membrane-bound hydrogen uptake in cyanobacteria.