Involved in isoprene degradation (PubMed:10094686, PubMed:10715003). Catalyzes the two-step NAD(+)-dependent oxidation of 2-glutathionyl-2-methylbut-3-en-1-ol (HGMB) to 2-glutathionyl-2-methylbut-3-enoate (GMBA) (PubMed:10094686). 2-glutathionyl-2-methylbut-3-en-1-ol + H2O + 2 NAD(+) = 2-glutathionyl-2-methylbut-3-enoate + 3 H(+) + 2 NADH 2-glutathionyl-2-methylbut-3-en-1-ol + NAD(+) = 2-glutathionyl-2-methylbut-3-enal + H(+) + NADH 2-glutathionyl-2-methylbut-3-enal + H2O + NAD(+) = 2-glutathionyl-2-methylbut-3-enoate + 2 H(+) + NADH Optimum pH is 9.0-10. Belongs to the short-chain dehydrogenases/reductases (SDR) family.