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Biomedical subjects

Michael J Page

Publications and source records attributed to Michael J Page.

11 recordsLinked to original sources
PubMed2006

Rhodium(I) and iridium(I) complexes of pyrazolyl-N-heterocyclic carbene ligands.

Several Rh(I) and Ir(I) complexes containing an N-heterocyclic carbene-pyrazolyl chelate ligand have been synthesised. Determination of the single-crystal X-ray structure of the Ir(I) complex showed a novel binding mode with the iridium centre coordinated to two ligands via two carbene donors in preference to one ligand forming the entropically favoured chelate. The hydrogenation activity of several of these complexes was investigated along with that of previously synthesised Rh(I) and Ir(I) complexes containing an analogous phosphine-pyrazolyl chelate.

Journal Article↗
PubMed2006

Cytochrome b(5) is a major reductant in vivo of human indoleamine 2,3-dioxygenase expressed in yeast.

The evolutionary relationship of indoleamine 2,3-dioxygenase (IDO) to some gastropod myoglobins suggests that IDO may undergo autoxidation in vivo such that one or more currently unidentified electron donors are required to maintain IDO heme iron in the active, ferrous state. To evaluate this hypothesis we have used yeast knockout mutants in combination with a recently developed yeast growth assay for IDO activity in vivo to demonstrate a role for cytochrome b(5) and cytochrome b(5) reductase in maintaining IDO activity in vivo.

Cytochrome-B(5) Reductase↗
PubMed2006

Conversion of trypsin into a Na(+)-activated enzyme.

Serine proteases of the chymotrypsin family show a dichotomous amino acid distribution for residue 225. Enzymes carrying Tyr at position 225 are activated by Na(+), whereas those carrying Pro are devoid of Na(+) binding and activation. Previous studies have demonstrated that the Y225P conversion is sufficient to abrogate Na(+) activation in several enzymes. However, the reverse substitution P225Y is necessary but not sufficient to introduce Na(+) binding and activation. Here we report that Streptomyces griseus trypsin, carrying Pro-225, can be engineered into a Na(+)-activated enzyme by replacing residues in the 170, 186, and 220 loops to those of coagulation factor Xa. The findings represent the first instance of an engineered Na(+)-activated enzyme and a proof of principle that should enable the design of other proteases with enhanced catalytic activity and allosteric regulation mediated by monovalent cation binding.

Enzyme Activation↗
PubMed2006

Proteomics: applications relevant to transfusion medicine.

With the completion of the human genome sequence, it is now possible to analyze the many individual components that comprise complex biologic systems. Despite this sequence data, understanding the biologic relationships of all proteins of a given cell or biologic sample (the proteome) is still an exceedingly difficult task. However, new technology developments mean that proteomics research can be used to investigate a variety of biologic systems. Already, these studies have given valuable insight for the development of improved diagnostic and therapeutic products. The present review aims to provide a basic understanding of proteomics research by discussing the methods used to study large numbers of proteins and by reviewing the application of proteomics methods to transfusion medicine.

Blood Proteins↗
PubMed2006

Role of Na+ and K+ in enzyme function.

Metal complexation is a key mediator or modifier of enzyme structure and function. In addition to divalent and polyvalent metals, group IA metals Na+ and K+ play important and specific roles that assist function of biological macromolecules. We examine the diversity of monovalent cation (M+)-activated enzymes by first comparing coordination in small molecules followed by a discussion of theoretical and practical aspects. Select examples of enzymes that utilize M+ as a cofactor (type I) or allosteric effector (type II) illustrate the structural basis of activation by Na+ and K+, along with unexpected connections with ion transporters. Kinetic expressions are derived for the analysis of type I and type II activation. In conclusion, we address evolutionary implications of Na+ binding in the trypsin-like proteases of vertebrate blood coagulation. From this analysis, M+ complexation has the potential to be an efficient regulator of enzyme catalysis and stability and offers novel strategies for protein engineering to improve enzyme function.

Animals↗
PubMed2003

Engineering the primary substrate specificity of Streptomyces griseus trypsin.

Streptomyces griseus trypsin (SGT) was chosen as a model scaffold for the development of serine proteases with enhanced substrate specificity. Recombinant SGT has been produced in a Bacillus subtilis expression system in a soluble active form and purified to homogeneity. The recombinant and native proteases have nearly identical enzymatic properties and structures. Four SGT mutants with alterations in the S1 substrate binding pocket (T190A, T190P, T190S, and T190V) were also expressed. The T190P mutant demonstrated the largest shift to a preference for Arg versus Lys in the P1 site. This was shown by a minor reduction in catalytic activity toward an Arg-containing substrate (k(cat) reduction of 25%). The crystal structures of the recombinant SGT and the T190P mutant in a complex with the inhibitor benzamidine were obtained at high resolution (approximately 1.9 A). The increase in P1 specificity, achieved with minimal effect on the catalytic efficiency, demonstrates that the T190P mutant is an ideal candidate for the design of additional substrate specificity engineered into the S2 to S4 binding pockets.

Amino Acid Substitution↗
PubMed2003

CD1d-expressing dendritic cells but not thymic epithelial cells can mediate negative selection of NKT cells.

Natural killer T (NKT) cells are a unique immunoregulatory T cell population that is positively selected by CD1d-expressing thymocytes. Previous studies have shown that NKT cells exhibit autoreactivity, which raises the question of whether they are subject to negative selection. Here, we report that the addition of agonist glycolipid alpha-galactosylceramide (alpha-GalCer) to a fetal thymic organ culture (FTOC) induces a dose-dependent disappearance of NKT cells, suggesting that NKT cells are susceptible to negative selection. Overexpression of CD1d in transgenic (Tg) mice results in reduced numbers of NKT cells, and the residual NKT cells in CD1d-Tg mice exhibit both an altered Vbeta usage and a reduced sensitivity to antigen. Furthermore, bone marrow (BM) chimeras between Tg and WT mice reveal that CD1d-expressing BM-derived dendritic cells, but not thymic epithelial cells, mediate the efficient negative selection of NKT cells. Thus, our data suggest that NKT cells developmentally undergo negative selection when engaged by high-avidity antigen or abundant self-antigen.

Animals↗
PubMed2002

Kottamides A-D: novel bioactive imidazolone-containing alkaloids from the New Zealand ascidian Pycnoclavella kottae.

Kottamides A-D (1-4), novel 2,2,5-trisubstituted imidazolone-containing alkaloids, were isolated from the New Zealand endemic ascidian Pycnoclavella kottae and structurally characterized using 15N natural abundance 2-D NMR in addition to standard spectroscopic methods. The kottamides exhibited anti-inflammatory and anti-metabolic activity as well as cytotoxicity toward tumor cell lines.

Alkaloids↗
PubMedDate not supplied

Factors affecting surgical risk in elderly patients with inflammatory bowel disease.

The operative treatment of elderly patients with inflammatory bowel disease (IBD) has often been avoided in favor of medical management because of a perceived increase in surgical risk. This study sought to define the following in the elderly IBD patient population: (1) the risk of surgical management and (2) those factors affecting risk. Thirty patients with IBD, aged 60 years or more, who were surgically managed by a single surgeon over a 10-year period, were retrospectively matched to 75 patients with IBD who were less than 60 years of age; patients were matched according to sex, date of surgery, and type of surgery performed. Regression analysis using generalized estimating equation methodology to account for the matched clusters of patients was performed to evaluate the effect of age group on the complication rate, operating room time, and length of hospital stay. Presence of comorbid conditions, surgical indications, prior surgery for IBD, and the use of immunosuppressive medications were studied in multivariate models, adjusting for age group. By means of univariate analysis, the odds of complications in elderly IBD patients were shown to be statistically higher than the odds seen in younger patients (47% vs. 20%, P = 0.01). Also observed in the elderly group were a longer length of hospital stay (11.5 days vs. 7.1 days, P = 0.001) and longer operating room time (249 minutes vs. 212 minutes, P = 0.02). Multivariate analysis revealed that the effect of age remained statistically significant, even when adjusted for potential confounding variables such as comorbidity, medications, date of diagnosis of IBD, and indications for surgery. The complication outcome was significantly associated with the surgical indication, with obstruction, fistula, and bleeding having increased odds of complications as compared with other indications (odds ratio = 1.7 vs. 4.2 vs. 7.2, respectively, P = 0.02). The length of hospital stay similarly was significantly associated with the surgical indication (fistula, 10.5 days vs. bleeding, 9.8 days vs. obstruction, 7.4 days vs. other, 9.3 days; P = 0.04) and a history of prior surgery. A significant interaction for length of hospital stay was present between age group and prior surgery status (with prior surgery: old, 18 days vs. young, 6.4 days, P = 0.0001; without prior surgery: old, 9.5 days vs. young 7.3 days, P = 0.10). Elderly patients with IBD have an increased rate of postoperative complications along with an increased length of hospital stay and increased operating room time. This effect of age persists when adjusted for comorbidity and immunosuppressive therapy. Complications are most dependent on surgical indications, with obstruction being the least and bleeding the worst predictive factors. The longest hospital stay is associated with patients who require surgery for fistulous disease and patients who have undergone previous surgery. The fact that the higher complication rate seen in older patients with IBD is associated with disease-defined surgical indications suggests that IBD in elderly patients may be more aggressive than what is observed in younger individuals.

Adolescent↗