Task: Class Definition Understanding (ontology: Sciences/Biology)

Which of the following definitions best describes 'androsterone dehydrogenase (A-specific) activity'?

A. Any of the spindle microtubules that come from each pole and overlap at the spindle midzone. This interdigitating structure consisting of antiparallel microtubules is responsible for pushing the poles of the spindle apart.
B. Catalysis of the reaction: NAD(P)+ + androsterone = NAD(P)H + H+ + 5-alpha-androstane-3,17-dione. The reaction is A-specific (i.e. the pro-R hydrogen is transferred from the 4-position of reduced nicotinamide cofactor) with respect to NAD(P)+.
C. A G protein-coupled receptor signaling pathway in which the receptor constitutively activates adenylate cyclase, without binding to an agonist.
D. Catalysis of the reaction: NAD(P)+ + androsterone = NAD(P)H + H+ + 5-alpha-androstane-3,17-dione. The reaction is B-specific (i.e. the pro-S hydrogen is transferred from the 4-position of reduced nicotinamide cofactor) with respect to NAD(P)+.

Answer: Catalysis of the reaction: NAD(P)+ + androsterone = NAD(P)H + H+ + 5-alpha-androstane-3,17-dione. The reaction is A-specific (i.e. the pro-R hydrogen is transferred from the 4-position of reduced nicotinamide cofactor) with respect to NAD(P)+.