The role of the active site residues in human galactokinase: implications for the mechanisms of GHMP kinases.

Galactokinase catalyses the phosphorylation of galactose at the expense of ATP. Like other members of the GHMP family of kinases it is postulated to function through an active site base mechanism in which Asp-186 abstracts a proton from galactose. This asparate residue was altered to alanine and to asparagine by site-directed mutagenesis of the corresponding gene. This resulted in variant enzyme with no detectable galactokinase activity. Alteration of Arg-37, which lies adjacent to Asp-186 and is postulated to assist the catalytic base, to lysine resulted in an active enzyme. However, alteration of this residue to glutamate abolished activity. All the variant enzymes, except the arginine to lysine substitution, were structurally unstable (as judged by native gel electrophoresis in the presence of urea) compared to the wild type. This suggests that the lack of activity results from this structural instability, in addition to any direct effects on the catalytic mechanism. Computational estimations of the pK(a) values of the arginine and aspartate residues, suggest that Arg-37 remains protonated throughout the catalytic cycle whereas Asp-186 has an abnormally high pK(a) value (7.18). Quantum mechanics/molecular mechanics (QM/MM) calculations suggest that Asp-186 moves closer to the galactose molecule during catalysis. The experimental and theoretical studies presented here argue for a mechanism in which the C-1-OH bond in the sugar is weakened by the presence of Asp-186 thus facilitating nucleophilic attack by the oxygen atom on the gamma-phosphorus of ATP.

Optimization of FRT Active Power Performance of a DFIG during Transient Grid Faults

Optimal fault ride-through (FRT) conditions for a doubly-fed induction generator (DFIG) during a transient grid fault are analyzed with special emphasis on improving the active power generation profile. The transition states due to crowbar activation during transient faults are investigated to exploit the maximum power during the fault and post-fault period. It has been identified that operating slip, severity of fault and crowbar resistance have a direct impact on the power capability of a DFIG, and crowbar resistance can be chosen to optimize the power capability. It has been further shown that an extended crowbar period can deliver enhanced inertial response following the transient fault. The converter protection and drive train dynamics have also been analyzed while choosing the optimum crowbar resistance and delivering enhanced inertial support for an extended crowbar period.

Characterisation of the active/de-active transition of mitochondrial complex I

Oxidation of NADH in the mitochondrial matrix of aerobic cells is catalysed by mitochondrial complex I. The regulation of this mitochondrial enzyme is not completely understood. An interesting characteristic of complex I from some organisms is the ability to adopt two distinct states: the so-called catalytically active (A) and the de-active, dormant state (D). The A-form in situ can undergo de-activation when the activity of the respiratory chain is limited (i.e. in the absence of oxygen). The mechanisms and driving force behind the A/D transition of the enzyme are currently unknown, but several subunits are most likely involved in the conformational rearrangements: the accessory subunit 39 kDa (NDUFA9) and the mitochondrially encoded subunits, ND3 and ND1. These three subunits are located in the region of the quinone binding site. The A/D transition could represent an intrinsic mechanism which provides a fast response of the mitochondrial respiratory chain to oxygen deprivation. The physiological role of the accumulation of the D-form in anoxia is most probably to protect mitochondria from ROS generation due to the rapid burst of respiration following reoxygenation. The de-activation rate varies in different tissues and can be modulated by the temperature, the presence of free fatty acids and divalent cations, the NAD/NADH ratio in the matrix, the presence of nitric oxide and oxygen availability. Cysteine-39 of the ND3 subunit, exposed in the D-form, is susceptible to covalent modification by nitrosothiols, ROS and RNS. The D-form in situ could react with natural effectors in mitochondria or with pharmacological agents. Therefore the modulation of the re-activation rate of complex I could be a way to ameliorate the ischaemia/reperfusion damage. This article is part of a Special Issue entitled: 18th European Bioenergetic Conference. Guest Editors: Manuela Pereira and Miguel Teixeira.

Transcending Boundaries of Creativity: Active learning in the Design Studio

This essay investigates the changing dynamics of interaction and paradigm of communication in the design studio. It analyses the process of practical implementation of interactive tools in architectural education which placed the
diversity of students’ cultural experiences, contextual awareness and individual interests as crucial resource for design innovation and inquiry. Building on Brian Lawson’s thesis on creativity in design thinking, this research project undertook
comprehensive investigation of students’ satisfaction of their roles in the studio and the room for liberal thought they are given to elaborate on genuine approach to architectural matters. The cyclical development of interactive learning strategy is explored through two different settings: first, it analyses architectural students’ position as passive/active in the studio, considering their relationships with tutors’ ideals; second, it reports on empirical strategy of students-led workshops at British schools of architecture, during which students have taken the lead of their creative design agenda. The practical implementation of interactive learning tools proved influential in helping students to personalize their design direction and to build a sense of confidence and independence.

The role of knowledge in the contraceptive behaviour of sexually active young people in state care

Aim: To analyse the role of sex-focused knowledge in the contraceptive behaviour of sexually active young people in state care.

Methods: The sample consisted of 19 care leavers (young people previously in state care) aged 18-22 years, 16 females and 3 males. In-depth interviewing was the method of data collection, and a qualitative strategy resembling modified analytical induction was used to analyse data.

Findings: Findings indicated that a lack of information was not the sole, or even the primary reason for engaging in unsafe sexual practices. Other factors such as ambivalence to becoming pregnant also featured in participants’ accounts. Several participants conveyed a relatively weak sense of agency about consistently using contraception. A small number of participants expressed a strong determination to avoid pregnancy, and these appeared to have a level of anxiety about becoming pregnant that motivated them to engage with knowledge about contraception and its use.

Conclusion: Lack of sex-focused information is just one aspect of a myriad of complex factors, including socioeconomic disadvantage and/or emotional deprivation, that influences contraceptive behaviour.

Seaborne trade and the commercialisation of fifteenth- and sixteenth-century Gaelic Ulster

This study considers the frequently stated claim that the economy of Gaelic- speaking lordships in Ulster during the fifteenth and sixteenth centuries was predominately pastoral anduncommercialised, by drawing on a variety of sources not usually combined. It proposes that the increased European demand for fish and the growth of the fish industry across northern Europe played a crucial role in stimulating trade between the coastal areas of Ulster on the one hand, and Britain and continental Europe on the other. This led to the establishment of permanent markets and towns, which joined at least two new inland towns in the southern parts of the province, bringing about a commercial presence in most of the Ulster lordships before 1600. Gaelic Lords consolidated this development by building castles and friaries at these fixed trading places.