Table 1.
Differentiation between ADH, MEOS, and catalase. Symbols for effects: (+), marginal; + low; ++, moderate; +++, high; ++++, very high. Abbreviations: ADH, alcohol dehydrogenase; Km, Michaelis-Menten constant; MEOS, microsomal ethanol-oxidizing system; N.D., not determined. The original table was published in a previous report [25] and is reproduced with permission of the Publisher Taylor & Francis (Didcot, UK).
| Characteristics | ADH | MEOS | Catalase |
|---|---|---|---|
| Intracellular localization | Cytosol | Endoplasmic reticulum | Peroxisomes |
| Co-factor | NAD+ | NADPH + H+ | N.D. |
| Co-substrate | None | Molecular oxygen | H2O2 |
| Reaction products | Acetaldehyde NADH + H+ |
Acetaldehyde NADP+, H2O |
Acetaldehyde H2O |
| Kinetics | |||
| Km (ethanol) | 0.5–2.0 mM | 7–11 mM | 0.6–10 mM |
| Km (O2) | N.D. | 8.3 μM | 50 μM |
| pH optimum | 11 | 6.9–7.5 | 5.5 |
| Inhibitory effect | |||
| Pyrazole (0.1 mM) | ++++ | 0 | (+) |
| Cyanide (0.1 mM) | N.D. | 0 | ++++ |
| Azide (0.1 mM) | 0 | 0 | ++++ |
| Substrate specificity | |||
| Methanol | ++ | ++ | ++++ |
| Ethanol | +++ | ++++ | ++++ |
| n-Propanol | ++++ | +++ | (+) |
| n-Butanol | ++++ | ++ | 0 |
| n-Pentanol | ++++ | + | 0 |
| i-Propanol | + | + | 0 |
| t-Butanol | 0 | + | 0 |
| Increase in activity following chronic ethanol consumption | 0 | ++++ | 0 |
| Enzyme isolation | + | + | + |
| Isoenzymes | + | + | + |