A limited survey of various conjugate gradient methods for solving complex matrix equations arising in electromagnetic wave interactions

There exists a wide variety of conjugate gradient algorithms for solving the complex matrix equations arising in electromagnetic wave interactions. The objective of this paper is to describe several of these algorithms which we have found to be computationally efficient. Both the strong and weak points of each version of the conjugate gradient method are presented. The principal conclusion is that at present, there is no single algorithm that provides an efficient solution for all types of problems. The computer programs corresponding to the algorithms discussed in the paper are provided in the Appendix.     

Electrochemically Treated Pencil Graphite Electrodes Prepared in One Step for the Electrochemical Determination of Paracetamol

This article reports the electrochemical determination of paracetamol (PC) in the presence of ascorbic acid (AA) and caffeine (CF) using an electrochemically treated pencil graphite electrode. In this study, we describe the use of an electrode prepared by overoxidation between 0.0 and +2.1 V for paracetamol determination. The electrochemically treated pencil graphite electrodes (ETPGEs) were prepared using a cyclic voltammetric method. The electrode was characterized by Scanning Electron Microscopy (SEM), Electrochemical Impedance Spectroscopy (EIS), and Resonance Raman Spectroscopy. The differences in oxidation peak potentials were large enough to determine PC in the presence of AA and CF. The electroactive areas of the bare electrode and 10 scan-ETPGE in 0.5 M H₂SO₄ were calculated to be 0.0031 and 0.0341 cm², respectively. The sensor (10 scan-ETPGE in 0.5 M H₂SO₄) was sensitive to the PC with 1.74 × 10^–7 M limits of detection (S/N = 3). Finally, the developed method and the prepared electrodes were used for determination of PC in the pharmaceutical samples.

     

Characterization of sulfhydryl oxidase from <Emphasis Type="Italic">Aspergillus tubingensis</Emphasis>

Background

Despite of the presence of sulfhydryl oxidases (SOXs) in the secretomes of industrially relevant organisms and their many potential applications, only few of these enzymes have been biochemically characterized. In addition, basic functions of most of the SOX enzymes reported so far are not fully understood. In particular, the physiological role of secreted fungal SOXs is unclear.

Results

The recently identified SOX from Aspergillus tubingensis (AtSOX) was produced, purified and characterized in the present work. AtSOX had a pH optimum of 6.5, and showed a good pH stability retaining more than 80% of the initial activity in a pH range 4-8.5 within 20 h. More than 70% of the initial activity was retained after incubation at 50 °C for 20 h. AtSOX contains a non-covalently bound flavin cofactor. The enzyme oxidised a sulfhydryl group of glutathione to form a disulfide bond, as verified by nuclear magnetic resonance spectroscopy. AtSOX preferred glutathione as a substrate over cysteine and dithiothreitol. The activity of the enzyme was totally inhibited by 10 mM zinc sulphate. Peptide- and protein-bound sulfhydryl groups in bikunin, gliotoxin, holomycin, insulin B chain, and ribonuclease A, were not oxidised by the enzyme. Based on the analysis of 33 fungal genomes, SOX enzyme encoding genes were found close to nonribosomal peptide synthetases (NRPS) but not with polyketide synthases (PKS). In the phylogenetic tree, constructed from 25 SOX and thioredoxin reductase sequences from IPR000103 InterPro family, AtSOX was evolutionary closely related to other Aspergillus SOXs. Oxidoreductases involved in the maturation of nonribosomal peptides of fungal and bacterial origin, namely GliT, HlmI and DepH, were also evolutionary closely related to AtSOX whereas fungal thioreductases were more distant.

Conclusions

AtSOX (55 kDa) is a fungal secreted flavin-dependent enzyme with good stability to both pH and temperature. A Michaelis-Menten behaviour was observed with reduced glutathione as a substrate. Based on the location of SOX enzyme encoding genes close to NRPSs, SOXs could be involved in the secondary metabolism and act as an accessory enzyme in the production of nonribosomal peptides.