PQQ and quinoprotein enzymes in microbial oxidations

Abstract Pyrroloquinoline quinone (PQQ) is found in a wide range of microorganisms, and several bacteria even excrete this compound into their culture medium when grown on alcohols. The existence of different classes of quinoprotein (PQQ-containing) enzymes is now well established (alcohol dehydrogenases, aldose (glucose) dehydrogenases, amine dehydrogenases and amine oxidases) while several other enzymes are suspected to be quinoproteins. In addition, many bacteria produce a quinoprotein apoenzyme, e.g., Escherichia coli and Pseudomonas testosteroni , producing glucose and ethanol dehydrogenase apoenzyme, respectively. It is unclear why these bacteria do not produce the holoenzyme form, but the apoenzymes have the ability to become functional, as was shown when the organisms were provided with PQQ. With this approach it could be demonstrated that E. coli has a non-phosphorylative route of glucose dissimilation via gluconate. Also, results with mixed cultures indicate that PQQ is a growth factor for certain bacteria under certain conditions. Despite the relatively high redox potential of the PQQ/PQQH₂ couple, quinoproteins transfer electrons to a variety of natural electron acceptors. Depending on the type of quinoprotein enzyme, the following components of the respiratory chain appear to be active: cytochrome c (sometimes with a copper protein as an intermediate), cytochrome b , and NADH dehydrogenase. PQQ is not restricted to a particular group of organisms, and reactions catalysed by quinoproteins can also be performed by NAD(P)-dependent or flavoprotein enzymes. Thus, these observations do not provide arguments for the view that quinoproteins have a unique role in microbial oxidations. Further comparative studies on oxidoreductases are necessary to reveal the special features of this novel group of enzymes.     

Characterisation of the PQQ cofactor radical in quinoprotein ethanol dehydrogenase of Pseudomonas aeruginosa by electron paramagnetic resonance spectroscopy

The binding pocket of the pyrroloquinoline quinone (PQQ) cofactor in quinoprotein alcohol dehydrogenases contains a characteristic disulphide ring formed by two adjacent cysteine residues. To analyse the function of this unusual structural motif we have investigated the wild-type and a double cysteine:alanine mutant of the quinoprotein ethanol dehydrogenase from Pseudomonas aeruginosa by electron paramagnetic resonance (EPR) spectroscopy. Thus, we have obtained the principal values for the full rhombic g-tensor of the PQQ semiquinone radical by high-field (94 GHz) EPR necessary for a discrimination of radical species in dehydrogenases containing PQQ together with other redox-active cofactors. Our results show that the characteristic disulphide ring is no prerequisite for the formation of the functionally important semiquinone form of PQQ.     

Neosporosis--the first decade of research

This paper reviews the history of Neospora caninum for the past decade, and provides a prospective for research for the next decade.     

Gene therapy: the first decade

Gene therapy promises to revolutionize medicine by treating the causes of disease rather than the symptoms. We are nearing the end of the first decade of gene therapy, and this article summarizes the approaches taken, results achieved, lessons learned and important recent developments. The early results on the clinical efficacy of gene therapies were disappointing, largely because the available gene-transfer vectors proved to be inadequate. Recently, however, clinical benefit has been clearly demonstrated and great progress made in selecting and improving vectors. There is now every prospect that the second decade will see gene therapy live up to its enormous potential.     

Ceramide kinase: the first decade

It has been some 20 years since the initial discovery of ceramide 1-phosphate (C1P) and nearly a decade since ceramide kinase (CERK) was cloned. Many studies have shown that C1P is important for membrane biology and for the regulation of membrane-bound proteins, and the CERK enzyme has appeared to be tightly regulated in order to control both ceramide levels and production of C1P. Furthermore, C1P made by CERK has emerged as a genuine signalling entity. However, it represents only part of the C1P pool that is available in the cell, therefore suggesting that alternative unknown C1P-producing mechanisms may also play a role. Recent technological developments for measuring complex sphingolipids in biological samples, together with the availability of Cerk-deficient animals as well as potent CERK inhibitors, have now provided new grounds for investigating C1P biology further. Here, we will review the current understanding of CERK and C1P in terms of biochemistry and functional implications, with particular attention to C1P produced by CERK.     

Abortion and the NHS: the first decade.

Analysis of statistics published since the Abortion Act showed that from 1972 about half the abortions carried out on residents of England and Wales had been performed within the National Health Service. Regional variations in the proportions of abortions performed within the NHS had persisted. In some health regions fewer abortions were being carried out than before. In 1975 about 40% of abortions on single women and women with no existing children were performed within the NHS. Trends in the concurrent sterilisation rate, gestational age at operation, duration of stay in hospital, and mortality and complication rates suggested a steady improvement in the effectiveness and efficiency of abortion services. Nevertheless, the NHS still compares poorly with the private sector and some other countries.     

The first decade of oligotrophication of Lake Constance

In Lake Constance, after several decades of cutrophication, a decrease in phosphorus loading over the last decade has lead to a partial recovery from eutrophication. Here we analyse the shift in the taxonomic composition of phytoplankton during the first decade of oligotrophication in Lake Constance. During the 1980s, spring total P concentrations decreased from ca. 130 to less than 50 ·l^–1. This decrease was reflected by an approximately proportional decrease in summer phytoplankton biomass while spring phytoplankton biomass seemed unresponsive. Major taxonomic changes occured during both growth seasons. In spring, the proportion of diatoms, green algae and Chrysophyta increased while the proportion of Cryptophyta decreased. The summer trend was very different: the relative importance of diatoms decreased and Cryptophyta and Chrysophyta increased, while Chlorophyta reached their peak around 1985. These trends are also analysed at the genus level. Comparison with taxonomic trends during the eutrophication period shows the expected reversals in most cases. Comparison with other lakes shows general similarities, with the notable exception that Planktothrix rubescens has never been important in Lake Constance. The increase of diatoms during spring is attributed to their improved competitive performance with increasing Si:P ratios. Their decrease during summer is explained by the increasing silicate removal from the epilimnion by increasing spring populations.     

The first decade of oligotrophication in Lake Constance

Phytoplankton biomass and species composition were measured with a relatively high temporal resolution (once or twice a week during the growing season) from 1979 to 1989 in Lake Constance/Überlingersee. Over this period soluble reactive phosphorus (SRP) concentrations during winter mixing were reduced by ca. 50% from 104 to 47 g 1^–1, which caused a prolongation and amplification of the epilimnetic P depletion during the growth period. Seasonal dynamics of phytoplankton reacted to the decrease of SRP in the following ways: (1) Algal biomass decreased at least proportionally to the winter SRP concentrations in summer, but not in spring and autumn when biomass fluctuated irregularly. (2) The peak of biomass concentration changed from summer to spring. (3) The earlier onset of epilimnetic P depletion during the season in recent years promoted a stronger growth of some pennate diatoms in spring. It caused an amplification of the silicon depletion in summer, which may cause still greater reduction of diatoms and total algal biomass in summer. (4) Reduction of algal biomass during the clear-water phase proper became shorter and less pronounced. (5) The temporal variability of algal biomass decreased in summer and autumn but not in spring. (6) Average cell sizes remained unchanged in summer and autumn but increased in spring during the beginning of oligotrophication. These results are largely in agreement with other studies on lake restoration and expectations derived from the PEG (Plankton Ecology Group) model (Sommer et al. 1986). They show that a 50% reduction of SRP concentrations during homothermy may have pronounced effects on seasonal dynamics of algal biomass in a large and deep lake. The algal response to the external change of SRP concentrations can be described by the Le Chatelier principle, implying that the internal structure of the system (e.g. species composition) changes in order to minimize the effect of the external pressure (e.g. reduction of total biomass). Suggestions are made as to how this system behaviour may emerge from local interactions.     

Transgenic RNAi in mouse oocytes: The first decade

RNA interference (RNAi), a sequence-specific mRNA degradation induced by double-stranded RNA (dsRNA), is a common approach employed to specifically silence genes. Experimental RNAi in plant and invertebrate models is frequently induced by long dsRNA. However, in mammals, short RNA molecules are used preferentially since long dsRNA can provoke sequence-independent type I interferon response. A notable exception are mammalian oocytes where the interferon response is suppressed and long dsRNA is a potent and specific trigger of RNAi. Transgenic RNAi is an adaptation of RNAi allowing for inducing sequence-specific silencing upon expression of dsRNA. A decade ago, we have developed a vector for oocyte-specific expression of dsRNA, which has been used to study gene function in mouse oocytes on numerous occasions. This review provides an overview and discusses benefits and drawbacks encountered by us and our colleagues while working with the oocytes-specific transgenic RNAi system.     

Conserving and restoring the Caicos pine forests: The first decade

The severe and rapid attack on the Caicos pine Pinus caribaea var. bahamensis(Pinaceae) by the nonnative invasive pine tortoise scale, Toumeyella parvicornis, has resulted in the death of most of the trees in the Turks and Caicos Islands(TCI) in just over a decade. Local and international conservation efforts have enabled the necessary multi-disciplinary research, data gathering, and monitoring to develop and implement a restoration strategy for this endemic tree from the Bahaman archipelago. The native plant nursery established on North Caicos and horticultural expertise acquired throughout the years were crucial to the successful rescue of Caicos pine saplings from the wild populations and cultivation of new saplings grown from locally sourced seeds. These saplings have been used to establish six Restoration Trial Plots on Pine Cay and a seed orchard on North Caicos in TCI. Core Conservation Areas(CCAs) for the Caicos pine forests have been identified and mapped. To date, forest within the Pine Cay CCA has been supplemented by planting more than 450 pine trees, which have survived at a high(>80%)rate.     

PQQ, the elusive coenzyme

The recently discovered redox coenzyme, PQQ (methoxatin), is widely distributed. Quantitation of protein-bound PQQ has been difficult, but unique redox cycling reactions, which reflect its striking biological properties, reveal trace amounts. PQQ is a potential target for drugs.     

Evaluation of multi- and inter-disciplinary research--the no-peer problem

The advent of peer review is relatively recent, yet it strongly influences the way we perform and evaluate research. The absence of the perfect peer for multi- and inter-disciplinary research makes evaluation more challenging. By recognizing and addressing the no-peer problem multi- and interdisciplinary research can be effectively communicated and evaluated.