Biliverdin reductase A activity

Focus: BVRA is an enzyme that reduces biliverdin to bilirubin. NADPH is consumed in the reaction.

Draft scope: There are some open questions in the right method for measuring BVRA activity. The question about blank activity will be discussed.

Variables:

• Total activity. Definition: Observed increase in absorbance (460 nm) per minute in reaction mix consisting of buffer, biliverdin, cytosol and NADPH.
• Blank. Definition: Observed increase in absorbance (460nm) per minute in reaction mix consisting of buffer, biliverdin and cytosol.
• Putatively specific activity. Definition: Total activity - blank.

Statement: Total activity is a better measure of actual BVRA activity than putatively specific activity.

Argumentation:

← Energy sources (NADPH) are available in the cytosol.

← Total activity is a specific measure of BVRA

← Activity ~0 if no cytosol (own observation). Even if not 0, this is the same for all samples.

→ When no cytosol, there is no BVRA

← Activity ~0 if no BV (own observation)

← It is unlikely that the reaction is unspecific

← Blank is large compared with total. Large variations in blank rate between the samples.