Three of these--ALDH1A1, ALDH1B1, and ALDH2--are most relevant to acetaldehyde oxidation (table 2).
It is likely that the ALDH1A1 and ALDH1B1 enzymes significantly contribute to acetaldehyde metabolism only in situations where ALDH2 is inactivated, either pharmacologically or because of the presence of the ALDH2*2 allele.
The Km values (3) of the ALDH1A1 and ALDH1B1 enzymes exceed those of the ALDH2 enzyme by at least 100-fold, and, thus, are not likely to be operating at full capacity when acetaldehyde levels are kept at the usual physiological state (i.e., below 5 pmol/L) (Klyosov et al.
Vasiliou's team studied colon cancers from 40 patients and found a form of this enzyme known as ALDH1B1 present in every colon cancer cell in 39 out of the 40 cases.
It appears that ALDH1B1 aids the development or growth of these cancer cells because it would not be present in every cell at such high levels if it were simply a byproduct of the cancer.
The team also is seeking to understand the substrate, inhibitors and activators of ALDH1B1.
(3) 22.7 mM corresponds to a blood alcohol concentration of 100 mg/dL Table 2 Kinetic Constants for Acetaldehyde oxidation by Human Aldehyde Dehydrogenases [V.sub.max] [K.sub.M] [V.sub.max] ([min.sup.-1] Enzyme ([micro]M) ([min.sup.-1]) [micro][M.sup.-1]) ALDH1A1 180 380 2.1 ALDH1B1
55 40 0.7 ALDH2*1 0.2 280 1400 ALDH2*2 1.4 20 14 (1) Data for ALDH1A1 and ALDH2*1 from Klyosov, 1996; data for ALDH2*2 oxidation of propionaldehyde from Farres et al., 1994 and data for ALDH1B1
from Stagos et al., 2010.