Biohydrogen Generation and Other Methods - Hydrogen Generation, Storage, and Utilization - page 63

TABLE 4.8 Classification of Hydrogenases

Features
Localization Classification Occurrence/Source Structure Function

Ni-Fe Anaerobic,

photosynthetic
bacteria,
cyanobacteria

Heterodimeric,
multimeric

Membrane-bound,
cytoplasmic,
periplasmic

Uptake of
hydrogen

Ni-Fe-Se Sulphate-reducing

bacteria,
methanogenes

Oligomeric Membrane-bound,

cytoplasmic

Oxidation of
hydrogen

Fe Photo-synthetic

bacteria, anaerobic
fermentative bacteria,
cyanobacteria, green
algae, protozoan

Monomeric,
heteromeric

Cytoplasmic,
mambrane-
bound,periplasmic
chloroplast,
hydrogenosomes

Production of
hydrogen

Metal-free Methanogens Monomeric Cytoplasmic Formation of

hydrogen

Source : Reproduced with permission from Das et al. [68].

dependent upon the presence of a hydrogen-producing enzyme. Hydroge-
nases and nitrogenases are the known enzymes which catalyze biological
hydrogen production. Hydrogenases are the key enzymes for the biological
hydrogen production, which can be classified as uptake hydrogenases and
reversible hydrogenases. Uptake hydrogenases, such as Ni-Fe hydrogenases
and Ni-Fe-Se hydrogenases, act as important catalysts for hydrogen con-
sumption as follows [23]:

− +

H → + 2 e 2 H

(4.10)

2

Reversible hydrogenases, as indicated by its name, have the ability to
produce H 2 as well as consume H 2 depending on the reaction condition,

H ↔ + 2 e

−

2 H

+ .

(4.11)

2

Despite increasingly conspicuous diversity in many respects, hydrogenase
can be classified broadly into three distinct classes: Ni-Fe hydrogenase,
Fe-hydrogenase, and metal-free hydrogenase [68]. Classification of hydrog-
enases is given in Table 4.8.

4.4.1 Biophotolysis of Water Using Microalgae

Biophotolysis is the action of light on biological systems that results in the
dissociation of a substrate usually water into molecular hydrogen and oxygen.
Photosynthetic bacteria (e.g., Rhodobactor) can use broad organic substrates,
including lactic and acetic acids, as the energy and carbon source under light