There is an astonishing array of microbial alcohol oxidoreductases. They display a wide variety of substrate specificities and they fulfill several vital but quite different physiological functions. Some of these enzymes are involved in the production of alcoholic beverages and of industrial solvents, others are important in the production of vinegar, and still others participate in the degradation of naturally occurring and xenobiotic aromatic compounds as well as in the growth of bacteria and yeasts on methanol. They can be divided into three major categories. (1) The NAD- or NADP-dependent dehydrogenases. These can in turn be divided into the group I long-chain (approximately 350 amino acid residues) zinc-dependent enzymes such as alcohol dehydrogenases I, II, and III of Saccharomyces cerevisiae or the plasmid-encoded benzyl alcohol dehydrogenase of Pseudomonas putida; the group II short-chain (approximately 250 residues) zinc-independent enzymes such as ribitol dehydrogenase of Klebsiella aerogenes; the group III "iron-activated" enzymes that generally contain approximately 385 amino acid residues, such as alcohol dehydrogenase II of Zymomonas mobilis and alcohol dehydrogenase IV of Saccharomyces cerevisiae, but may contain almost 900 residues in the case of the multifunctional alcohol dehydrogenases of Escherichia coli and Clostridium acetobutylicum. The aldehyde/alcohol oxidoreductase of Amycolatopsis methanolica and the methanol dehydrogenases of A. methanolica and Mycobacterium gasti are 4-nitroso-N,N-dimethylaniline-dependent nicotinoproteins. (2) NAD(P)-independent enzymes that use pyrroloquinoline quinone, haem or cofactor F420 as cofactor, exemplified by methanol dehydrogenase of Paracoccus denitrificans, ethanol dehydrogenase of Acetobacter and Gluconobacter spp. and the alcohol dehydrogenases of certain archaebacteria. (3) Oxidases that catalyze an essentially irreversible oxidation of alcohols, such as methanol oxidase of Hansenula polymorpha and probably the veratryl alcohol oxidases of certain fungi involved in lignin degradation. This review deals mainly with those enzymes for which complete amino acid sequences are available. The discussion focuses on a comparison of their primary, secondary, tertiary, and quaternary structures and their catalytic mechanisms. The physiological roles of the enzymes and isoenzymes are also considered, as are their probable evolutionary relationships.

Rhodococci display a diverse range of metabolic capabilities and they are a ubiquitous feature of many environments. They are able to degrade short-chain, long-chain, and halogenated hydrocarbons, and numerous aromatic compounds, including halogenated and other substituted aromatics, heteroaromatics, hydroaromatics, and polycyclic aromatic hydrocarbons. They possess a wide variety of pathways for degrading and modifying aromatic compounds, including dioxygenase and monooxygenase ring attack, and cleavage of catechol by both ortho- and meta-routes, and some strains possess a modified 3-oxoadipate pathway. Biotransformations catalyzed by rhodococci include steroid modification, enantioselective synthesis, and the transformation of nitriles to amides and acids. Tolerance of rhodococci to starvation, their frequent lack of catabolite repression, and their environmental persistence make them excellent candidates for bioremediation treatments. Some strains can produce poly(3-hydroxyalkanoate)s, others can accumulate cesium, and still others are the source of useful enzymes such as phenylalanine dehydrogenase and endoglycosidases. Other actual or potential applications of rhodococci include desulfurization of coal, bioleaching, use of their surfactants in enhancement of oil recovery and as industrial dispersants, and the construction of biosensors.

Bryophyllum fedtschenkoi is a Crassulacean acid metabolism plant whose phosphoenolpyruvate carboxylase is regulated by reversible phosphorylation in response to a circadian rhythm. A partially purified protein kinase phosphorylated phosphoenolpyruvate carboxylase in vitro with a stoichiometry approaching one per subunit and caused a concomitant 5‐ to 10‐fold decrease in the sensitivity of the carboxylase to inhibition by malate. The sites phosphorylated in vitro were identical to those phosphorylated in intact tissue. The activity of the protein kinase was controlled in a circadian fashion. During normal diurnal cycles, kinase activity appeared between 4 and 5 h after the onset of darkness and disappeared 2‐‐‐‐3 h before the end of darkness. Kinase activity displayed circadian oscillations in constant environmental conditions. The activity of protein phosphatase 2A, which dephosphorylates phosphoenolpyruvate carboxylase, did not oscillate. Treatment of detached leaves with the protein synthesis inhibitors puromycin and cycloheximide blocked the nocturnal appearance of the protein kinase activity, maintained phosphoenolypyruvate carboxylase in the dephosphorylated state and blocked the circadian rhythms of CO2 output that is observed in constant darkness and CO2‐free air. The simplest explanation of the data is that there is a circadian rhythm in the synthesis of phosphoenolpyruvate carboxylase kinase.

Phosphoenolpyruvate carboxylase of Bryophyllum fedtschenkoi was shown to exist in two forms: a night form, which is phosphorylated and has low sensitivity to inhibition by malate, and a day form, which is dephosphorylated and 10 times more sensitive to malate. The day and night forms of the enzyme were purified retaining their distinct malate sensitivities and phosphorylation states. The purified enzymes contained a major protein (subunit Mr 112,000) and a minor protein (subunit Mr 123,000). The two polypeptides appeared to have closely related amino acid sequences and were present in a similar ratio in extracts that had been prepared rapidly. The phosphate present in the night form of the enzyme was covalently bound to serine. It was not a catalytic intermediate. Alkaline phosphatase removed the phosphate group in vitro and increased the malate sensitivity of the enzyme to that observed for the day form. Both the day and night forms of the enzyme were probably tetramers, and their apparent Mr was lowered by the presence of malate, but was unaffected by Mg2+ ions, EDTA, a rise in pH or a 10-fold change in enzyme concentration. The rapid loss of malate sensitivity, observed in extracts of leaves prepared during the day and at night, was shown to be due to proteolysis of the enzyme. It was slowed in the presence of malate and by phosphorylation of the enzyme.

1. Bacterium N.C.I.B. 8250 was grown on dl-mandelate, benzyl alcohol, benzoyl-formate, benzaldehyde and benzoate and also on 2-hydroxy, 4-hydroxy, 3,4-dihydroxy and 4-hydroxy-3-methoxy analogues of these compounds. The enzymic complements of the cells were determined and the specificities of some of the enzymes examined. 2. Growth on mandelate or benzoylformate induces l-mandelate dehydrogenase, benzoylformate decarboxylase, benzyl alcohol dehydrogenase and a heat-stable as well as a heat-labile benzaldehyde dehydrogenase. Growth on benzyl alcohol or benzaldehyde induces benzyl alcohol dehydrogenase and the heat-labile benzaldehyde dehydrogenase. 3. The enzymes of the mandelate-to-benzoate pathway are non-specifically active on, and induced by, all the substituted analogues that support growth. 4. Benzoate oxidase is induced by growth on benzoate or on 2-hydroxybenzoate. 2-Hydroxybenzoate hydroxylase, 4-hydroxybenzoate hydroxylase and 4-hydroxy-3-methoxybenzoate O-demethylase are induced only by growth on homologous substrates. 5. The results of the investigation are discussed with regard to the possible regulation of the enzyme systems.