Secondary alcohol dehydrogenase catalyzes the reduction of exogenous acetone to 2‐propanol in Trichomonas vaginalis

Abstract

Secondary alcohols such as 2-propanol are readily produced by various anaerobic bacteria that possess secondary alcohol dehydrogenase (S-ADH), although production of 2-propanol is rare in eukaryotes. Specific bacterialtype S-ADH has been identified in a few unicellular eukaryotes, but its function is not known and the production of secondary alcohols has not been studied. We purified and characterized S-ADH from the human pathogen Trichomonas vaginalis. The kinetic properties and thermostability of T. vaginalis S-ADH were comparable with bacterial orthologues. The substantial activity of S-ADH in the parasite's cytosol was surprising, because only low amounts of ethanol and trace amounts of secondary alcohols were detected as metabolic end products. However, S-ADH provided the parasite with a high capacity to scavenge and reduce external acetone to 2-propanol. To maintain redox balance, the demand for reducing power to metabolize external acetone was compensated for by decreased cytosolic reduction of pyruvate to lactate and by hydrogenosomal metabolism of pyruvate. We speculate that hydrogen might be utilized to maintain cytosolic reducing power. The high activity of Tv-S-ADH together with the ability of T. vaginalis to modulate the metabolic fluxes indicate efficacious metabolic responsiveness that could be advantageous for rapid adaptation of the parasite to changes in the host environment.

A Nonmitochondrial Hydrogen Production in Naegleria gruberi

“…As a result, we found that N. gruberi cells are able to produce ∼6 nmol of hydrogen/min/10 7 cells (table 2). This level is about three times higher than hydrogen production observed in microaerophilic organisms G. intestinalis (2 nmol/min/10 7 cells; Lloyd et al 2002) and about five times lower than in T. vaginalis (Sutak et al 2012). …”

“…Even in T . vaginalis , some of the [FeFe]-hydrogenases might be present outside of hydrogenosomes (Sutak et al 2012); however, hydrogenase maturases were found exclusively within organelles, thus far.…”

Unexpected properties of NADP-dependent secondary alcohol dehydrogenase (ADH-1) in Trichomonas vaginalis and other microaerophilic parasites

“…Indeed, ethanol is only formed under strictly anaerobic condition (Ellis et al, 1992) and the inhibitory effect of CoA on ADH-1 activity also suggests a link to hydrogenosomal pathways. Accordingly, Sutak et al (2012), observed a major shift in the composition of metabolic end products when acetone was added to the growth medium, production of acetate being enhanced and that of lactate being decreased. However, as T .…”

“…While we were preparing the present manuscript, a study was published by Sutak et al describing purification of ADH-1 from T . vaginalis cell extract and its subsequent characterisation (Sutak et al, 2012). Interestingly, the determined kinetic parameters of the enzyme differ in various aspects form those presented in this study.…”

“…Further, in our hands, the measured V max’s for acetaldehyde, acetone, and 2-propanol were quite similar (Table 1), whereas acetone was almost ten times faster reduced than 2-propanol oxidised when using ADH-1 purified from T . vaginalis extract (Sutak et al, 2012). Since the measured K m’s for acetaldehyde, acetone, and NADPH are much more congruent between both studies, it is likely that the observed discrepancies are brought about by post-translational modifications, either in E .…”