Activation of biliverdin-IXalpha reductase by inorganic phosphate and related anions.
The effect of pH on the initial-rate kinetic behaviour of BVR-A (biliverdin-IXalpha reductase) exhibits an alkaline optimum with NADPH as cofactor, but a neutral optimum with NADH as cofactor. This has been described as dual cofactor and dual pH dependent behaviour; however, no mechanism has been described to explain this phenomenon. We present evidence that the apparent peak of activity observed at neutral pH with phosphate buffer and NADH as cofactor is an anion-dependent activation, where inorganic phosphate apparently mimics the role played by the 2'-phosphate of NADPH in stabilizing the interaction between NADH and the enzyme. The enzymes from mouse, rat and human all exhibit this behaviour. This behaviour is not seen with BVR-A from Xenopus tropicalis or the ancient cyanobacterial enzyme from Synechocystis PCC 6803, which, in addition to being refractory to activation by inorganic phosphate, are also differentiated by an acid pH optimum with both nicotinamide nucleotides.
Franklin
Edward
E
School of Biochemistry and Immunology, Trinity College, Dublin 2, Ireland. efrankli@tcd.ie
Browne
Seamus
S
Hayes
Jerrard
J
Boland
Coilin
C
Dunne
Aisling
A
Elliot
Gordon
G
Mantle
Timothy J
TJ
D000818:Animals; D000838:Anions / Q000378:metabolism*; D001663:Bilirubin / Q000737:chemistry / Q000378:metabolism; D001664:Biliverdine / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D004789:Enzyme Activation; D004795:Enzyme Stability; D006801:Humans; D006863:Hydrogen-Ion Concentration; D051379:Mice; D008807:Mice, Inbred BALB C; D008958:Models, Molecular; D015394:Molecular Structure; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000737:chemistry / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D051381:Rats; D012474:Salmon / Q000378:metabolism; D046939:Synechocystis / Q000201:enzymology
D000838:Anions; D010710:Phosphates; D009243:NAD; D009249:NADP; D044925:Oxidoreductases Acting on CH-CH Group Donors; C019789:biliverdin reductase; D001664:Biliverdine; D001663:Bilirubin