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Three allyl-alcohol-resistant mutants were isolated in the dimorphic fungus Mucor rouxii and characterized with regard to their alcohol dehydrogenase (ADH) activity in vitro and in vivo as well as their ability to execute the morphological alternatives of dimorphism under different environmental stimuli, either in the absence or in the presence of oxygen. These studies indicated that fermentation and yeast-cell development are independent events and that ADH activity is essential for growth of the fungus in the absence of oxygen. Heterokaryon construction and analysis indicated that in the three mutant strains the corresponding genetic alterations are recessive nuclear mutations which behave as allelic in complementation tests.

Invasive candidiasis is associated with high mortality in immunocompromised and hospitalized patients. Candida albicans is the main pathological agent followed by Candida glabrata, Candida krusei, Candida parapsilosis, and Candida tropicalis. These pathogens colonize different host tissues in humans as they are able to neutralize the reactive species generated from nitrogen and oxygen during the respiratory burst. Among the enzymatic mechanisms that Candida species have developed to protect against free radicals are enzymes with antioxidant and immunodominant functions such as flavohemoglobins, catalases, superoxide dismutases, glutathione reductases, thioredoxins, peroxidases, heat-shock proteins, and enolases. These mechanisms are under transcriptional regulation by factors such as Cta4p, Cwt1p, Yap1p, Skn7p, Msn2p, and Msn4p. However, even though it has been proposed that all Candida species have similar enzymatic systems, it has been observed that they respond differentially to various types of stress. These differential responses may explain the colonization of different organs by each species. Here, we review the enzymatic mechanisms developed by C. albicans and C. glabrata species in response to oxidative and nitrosative stresses. Lack of experimental information for other pathogenic species limits a comparative approach among different organisms.

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The protozoan parasite Entamoeba histolytica is an ancient eukaryotic cell that shows morphologically atypical organelles and differs metabolically from higher eukaryotic cells. The aim of this study was to determine the subcellular localization of ameba NAD+-dependent alcohol dehydrogenase (ADH2). The enzyme activity was present in soluble and mainly in particulate material whose density was 1.105 in a sucrose gradient. By differential centrifugation, most of the ADH activity sedimented at 160,000 g (160,000-g pellet), similar to the Escherichia coli polymeric ADHE. In the Coomassie staining of the 160,000-g pellet analyzed by electrophoresis, a 96-kDa protein was more prominent than in other fractions; this band was recognized by antibodies against Lactococcus lactis ADHE. By gold labeling, the antibodies recognized the granular material that mainly constitutes the 160,000-g pellet and a material that sedimented along with the internal membrane vesicles. By negative staining, the 160,000-g fraction showed helical rodlike structures with an average length of 103 nm; almost no membrane vesicles were observed in this pellet. In internal membrane fractions, no rodlike structures were found, but protomerlike round structures were observed. These results indicate that the main amebic NAD+-dependent ADH2 activity is naturally organized as rodlike helical particles, similar to bacterial ADHE. Detection of ADH2 in membrane fractions might be explained by cosedimentation of the multimeric ADH during membrane purification.