Malic acid is a key flavour component of many fruits and vegetables. There is significant interest in technologies for monitoring its concentration, particularly in winemaking. In this review we systematically and comprehensively chart progress in the development of enzyme-based amperometric biosensors for malic acid. We summarise the components and analytical parameters of malic acid sensors that have been reported over the past four decades, discussing their merits and pitfalls in terms of accuracy, sensitivity, linear range, response time and stability. We discuss how advances in electrode materials, electron mediators and the use of coupled enzymes have improved sensitivity and minimised interference, but also uncover a trade-off between sensitivity and linear range. A particular focus of our review is the three types of malate oxidoreductase enzyme that have been used in malic acid biosensors. We describe their different properties and conclude that identifying and/or engineering superior alternatives will be a key future direction for improving the commercial utility of malic acid biosensors.

A generalized model for electron (e(-) ) transport limited C(4) photosynthesis of NAD-malic enzyme and NADP-malic enzyme subtypes is presented. The model is used to review the thylakoid stoichiometries in vivo under strictly limiting light conditions, using published data on photosynthetic quantum yield and on photochemical efficiencies of photosystems (PS). Model review showed that cyclic e(-) transport (CET), rather than direct O(2) photoreduction, most likely contributed significantly to the production of extra ATP required for the C(4) cycle. Estimated CET, and non-cyclic e(-) transport supporting processes like nitrogen reduction, accounted for ca. 45 and 7% of total photosystem I (PSI) e(-) fluxes, respectively. The factor for excitation partitioning to photosystem II (PSII) was ca. 0.4. Further model analysis, in terms of the balanced NADPH: ATP ratio required for metabolism, indicated that: (1) the Q-cycle is obligatory; (2) the proton: ATP ratio is 4; and (3) the efficiency of proton pumping per e(-) transferred through the cytochrome b(6) /f complex is the same for CET and non-cyclic pathways. The analysis also gave an approach to theoretically assess CO(2) leakiness from bundle-sheath cells, and projected a leakiness of 0.07-0.16. Compared with C(3) photosynthesis, the most striking C(4) stoichiometry is its high fraction of CET.

Malate dehydrogenases (MDHs) are specific class of ubiquitous and multimeric oxidative decarboxylases with well conserved amino acid sequences in structurally important regions and with similar overall structural topology. They mostly use malate or oxaloacetate as substrates to generate pyruvate and utilize preferentially NADP or NAD as cofactor. Among species and even within an organism they differ in their subcellular localization and specificity for the cofactor. Comparison across microbial, plant and animal kingdoms show that MDHs were able to adopt tissue-, species- or environmental-specific functions while still keeping main structural features. Although basic principles of MDH regulation are similar to other enzymes and include oligomerization, cofactor binding, divalent cation availability, some of MDH enzymes are regulated also at different levels involving control of hysteresis, protein-protein interaction and gene expression. In this review we concentrate on those aspects of MDH function and regulation in animals that are specifically associated with cell differentiation and proliferation, ontogenic development, hormonal control, and partly with diseases. Accenting these aspects of MDHs provides emerging and new views on their regulatory function in complex eukaryotic metazoan organisms that goes beyond their classical role in basic metabolism.

暂无摘要。

Recently collected data on the Venezuelan species of the genus Brumptomyia are used to produce an updated review of these sandflies. At present, four species are recognized in Venezuela: B. devenanzii, B. beaupertuyi, B. avellari and B. pintoi. A key for the males is given and the geographical distribution of each of these species is outlined. The previously unknown female of B. devenanzii is described, the male is re-described, and the genetic variability (based on 11 enzymatic loci) of this species and of B. beaupertuyi (a sympatric species in Rancho Grande, the type locality of B. devenanzii) are reported. Fixed allelic differences in one diagnostic locus (adenylate kinase; Ak), between sympatric and allopatric populations, allowed for the unequivocal separation of both sexes of B. beaupertuyi from those of B. devenanzii. Significant inter-specific differences were also detected in the allele frequencies of malate dehydrogenase (Mdh-2) and decarboxylating malate dehydrogenase (Me). For B. devenanzii, mean heterozygosity and mean number of alleles per locus ranged from 2.0%-3.1% and 1.1-1.5, respectively. The corresponding values for B. beaupertuyi were 3.8% and 1.2.

暂无摘要。

暂无摘要。

This review examines the mechanism of translocation of cytoplasmically synthesized proteins into mitochondria. Approximately 10% of the mitochondrial proteins are synthesized within the organelles while most mitochondrial proteins are coded for by nuclear genes and synthesized on cytoplasmic ribosomes. Those mitochondrial proteins synthesized on cytoplasmic ribosomes have to be transferred at some point into one of the mitochondrial compartments, a process which would require their insertion through one or both mitochondrial membranes. Data accumulated during the past five years indicate that the cytoplasmically synthesized mitochondrial proteins are synthesized on free polysomes then released into the cytoplasm. Most of the proteins examined so far are synthesized in the cytoplasm as larger precursors whose conformations may differ from the conformations of their respective mature forms. These precursor proteins become translocated into mitochondrial post-translationally and processed to their mature forms either during or immediately following translocation into the organelles. The translocation step appears to require mitochondrial ATP. Some processing activities have been localized in the matrix fractions of mitochondria from liver and yeast and they appear to be associated with soluble endopeptidases which act selectively on precursors of mitochondrial proteins. Although it is not clear how the precursor proteins interact with or recognize mitochondrial membranes, studies in yeast indicate that the interactions occur at specific regions on the other mitochondrial membranes.

暂无摘要。

暂无摘要。