50
V. K. Kannaujiya et al.
3.5.2 Heme to Biliverdin IXα
The biosynthesis from heme to biliverdin IXα (BV) is catalyzed by heme oxygenase (HOs) (Dammeyer and Frankenberg-Dinkel 2008). Heme oxygenase enzyme is
catalytically triggered by molecular oxygen and reducing electrons (Kannaujiya et al.
2017c, d). Sometimes, biliverdin IXα is also converted into bilirubin IXα by catalysis of biliverdin reductase recorded in most of the fresh and marine cyanobacteria
(Kannaujiya et al. 2017c). However, prominent functionality of enzymes requires
reducing sugar such as NAD (Sugishima et al. 2005) and reduced methine bridge
located between B and C of biliverdin (Overkamp et al. 2014).
3.5.3 Biliverdin IXα to Phycobilins
Phycobilins are initially formed by the cleavage of carbon bridges in protoheme
while the reconstruction of pyrrole rings (A or D) occurs by the action of bilin
reductases enzymes (Stadnichuk and Tropin 2017). In the next step of conversion,
FDBR family gene (ferredoxin-dependent bilin reduction) (Frankenberg et al. 2001)
produces certain enzymes such as 15, 16-dihydrobiliverdin: ferredoxin oxidoreductase (pebA), phycoerythrobilin: ferredoxin oxidoreductase (pebB), phycocyanobilin:
ferredoxin oxidoreductase (pcyA) and phycoerythrobilin synthase, (pebS) and heme
oxygenase (HO) play a distinctive role in the conversion of BV to phycyanobilin
(PcyA) and phycoerythrobilin (Peb A, B) (Beale and Cornejo 1991, Dammeyer et al.
2008, Scheer et al. 2015). Heme oxygenase is crucially dependent on oxygen concentration for optimum activity. In the cyanobacterium Synechocystis 6803, two isoform
genes ho1 and ho2 have been recognized which encodes heme oxygenase with 50%
similarity between amino acids (Sugishima et al. 2005, Aoki et al. 2011, Fujita et al.
2015). The HO2 also shows potential catalytic activity with oxygen as compared to
HO1. However, HO is also found in anaerobic bacterium Clostridium perfringens
and Clostridium tetani (Brüggemann et al. 2004). In addition, the catalytic products
of heme oxygenase, biliverdin IXα, and its derivative bilirubin play as a potent oxidative inhibitor (Wegiel et al. 2014). The crystallography analysis of α helix exhibits the
presence of highly conserved residues including His and Asp which provide native
polar contacts in the BV IXα conversion to PC (Unno et al. 2015) (Fig. 3.3). PebS is a
catalytic protein which is composed of 233 different amino acids that regulate alternate pathway for the conversion from BV to PEB including intermediate products 15,
16-DHBV (Martiny et al. 2006). However, other intermediate components like PVB
are produced by molecular isomerization of cystein-84 residue by the activity of lyase
enzymes PecE/F in Mastigocladus laminosus (Böhm et al. 2007). The activities of
bilin lyase enzymes ensure the proper functionality of Cyst integrated chromophore
in bilin proteins (Arciero et al. 1988). The isomerization is a key feature of lyase
enzyme which converts PVB into PCB and PUB into PEB by isomerization of native
chromophores (Blot et al. 2009). Methylation of asparagine amino acid is commonly
V. K. Kannaujiya et al.
3.5.2 Heme to Biliverdin IXα
The biosynthesis from heme to biliverdin IXα (BV) is catalyzed by heme oxygenase (HOs) (Dammeyer and Frankenberg-Dinkel 2008). Heme oxygenase enzyme is
catalytically triggered by molecular oxygen and reducing electrons (Kannaujiya et al.
2017c, d). Sometimes, biliverdin IXα is also converted into bilirubin IXα by catalysis of biliverdin reductase recorded in most of the fresh and marine cyanobacteria
(Kannaujiya et al. 2017c). However, prominent functionality of enzymes requires
reducing sugar such as NAD (Sugishima et al. 2005) and reduced methine bridge
located between B and C of biliverdin (Overkamp et al. 2014).
3.5.3 Biliverdin IXα to Phycobilins
Phycobilins are initially formed by the cleavage of carbon bridges in protoheme
while the reconstruction of pyrrole rings (A or D) occurs by the action of bilin
reductases enzymes (Stadnichuk and Tropin 2017). In the next step of conversion,
FDBR family gene (ferredoxin-dependent bilin reduction) (Frankenberg et al. 2001)
produces certain enzymes such as 15, 16-dihydrobiliverdin: ferredoxin oxidoreductase (pebA), phycoerythrobilin: ferredoxin oxidoreductase (pebB), phycocyanobilin:
ferredoxin oxidoreductase (pcyA) and phycoerythrobilin synthase, (pebS) and heme
oxygenase (HO) play a distinctive role in the conversion of BV to phycyanobilin
(PcyA) and phycoerythrobilin (Peb A, B) (Beale and Cornejo 1991, Dammeyer et al.
2008, Scheer et al. 2015). Heme oxygenase is crucially dependent on oxygen concentration for optimum activity. In the cyanobacterium Synechocystis 6803, two isoform
genes ho1 and ho2 have been recognized which encodes heme oxygenase with 50%
similarity between amino acids (Sugishima et al. 2005, Aoki et al. 2011, Fujita et al.
2015). The HO2 also shows potential catalytic activity with oxygen as compared to
HO1. However, HO is also found in anaerobic bacterium Clostridium perfringens
and Clostridium tetani (Brüggemann et al. 2004). In addition, the catalytic products
of heme oxygenase, biliverdin IXα, and its derivative bilirubin play as a potent oxidative inhibitor (Wegiel et al. 2014). The crystallography analysis of α helix exhibits the
presence of highly conserved residues including His and Asp which provide native
polar contacts in the BV IXα conversion to PC (Unno et al. 2015) (Fig. 3.3). PebS is a
catalytic protein which is composed of 233 different amino acids that regulate alternate pathway for the conversion from BV to PEB including intermediate products 15,
16-DHBV (Martiny et al. 2006). However, other intermediate components like PVB
are produced by molecular isomerization of cystein-84 residue by the activity of lyase
enzymes PecE/F in Mastigocladus laminosus (Böhm et al. 2007). The activities of
bilin lyase enzymes ensure the proper functionality of Cyst integrated chromophore
in bilin proteins (Arciero et al. 1988). The isomerization is a key feature of lyase
enzyme which converts PVB into PCB and PUB into PEB by isomerization of native
chromophores (Blot et al. 2009). Methylation of asparagine amino acid is commonly