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Biomedical subjects

J A Jenkins

Publications and source records attributed to J A Jenkins.

At least 19 recordsLinked to original sources
PubMed1991

Protein engineering to change thermal stability for food enzymes.

In this review we have briefly indicated how the present state of knowledge allows proteins to be mutated to increase or decrease stability. We have discussed experiments on both model proteins and those of relevance to the food industry, and show how hydrophobic forces are a major driving force for folding as well as having a major role in thermostability. We have also indicated the large contribution that hydrogen bonding, electrostatic interactions and, in a less well predicted way, disulphide bridges make to thermostability.

Enzyme Stability↗
PubMed1991

Clinical evaluation of the effects of storage time and irradiation on transfused platelets.

Platelet concentrates stored for up to 5 days at room temperature or irradiated with 15 Gy immediately prior to transfusion were evaluated for their ability to increase the platelet count in thrombocytopenic patients. Platelets irradiated with a dose of 15 Gy immediately prior to transfusion achieved corrected increments (CI) at 1 and 20 h after transfusion no different from those achieved by non-irradiated platelets. Storage for 5 days reduced the mean 1-hour CI to 5.7 compared with a mean of 12.3 achieved by platelets transfused after only 1-day storage (p = 0.008). Similarly, the frequency of a repeat transfusion being indicated within 24 h increased with increasing storage time (p = 0.005).

Blood Platelets↗
PubMed1990

X-ray analyses of aspartic proteinases. The three-dimensional structure at 2.1 A resolution of endothiapepsin.

The molecular structure of endothiapepsin (EC 3.4.23.6), the aspartic proteinase from Endothia parasitica, has been refined to a crystallographic R-factor of 0.178 at 2.1 A resolution. The positions of 2389 protein non-hydrogen atoms have been determined and the present model contains 333 solvent molecules. The structure is bilobal, consisting of two predominantly beta-sheet domains that are related by an approximate 2-fold axis. Of approximately 170 residues, 65 are topologically equivalent when one lobe is superimposed on the other. Twenty beta-strands are arranged as five beta-sheets and are connected by regions involving 29 turns and four helices. A central sheet involves three antiparallel strands from each lobe organized around the dyad axis. Each lobe contains a further local dyad that passes through two sheets arranged as a sandwich and relates two equivalent motifs of four antiparallel strands (a, b, c, d) followed by a helix or an irregular helical region. Sheets 1N and 1C, each contain two interpenetrating psi structures contributed by strands c,d,d' and c',d',d, which are related by the intralobe dyad. A further sheet, 2N or 2C, is formed from two extended beta-hairpins from strands b,c and b',c' that fold above the sheets 1N and 1C, respectively, and are hydrogen-bonded around the local intralobe dyad. Asp32 and Asp215 are related by the interlobe dyad and form an intricate hydrogen-bonded network with the neighbouring residues and comprise the most symmetrical part of the structure. The side-chains of the active site aspartate residues are held coplanar and the nearby main chain makes a "fireman's grip" hydrogen-bonding network. Residues 74 to 83 from strands a'N and b'N in the N-terminal lobe form a beta-hairpin loop with high thermal parameters. This "flap" projects over the active site cleft and shields the active site from the solvent region. Shells of water molecules are found on the surface of the protein molecule and large solvent channels are observed within the crystal. There are only three regions of intermolecular contacts and the crystal packing is stabilized by many solvent molecules forming a network of hydrogen bonds. The three-dimensional structure of endothiapepsin is found to be similar to two other fungal aspartic proteinases, penicillopepsin and rhizopuspepsin. Even though sequence identities of endothiapepsin with rhizopuspepsin and penicillopepsin are only 41% and 51%, respectively, a superposition of the three-dimensional structures of these three enzymes shows that 237 residues (72%) are within a root-mean-square distance of 1.0 A.

Amino Acid Sequence↗
PubMed1990

Membrane damage to Escherichia coli and bactericidal kinetics by the alternative complement pathway of channel catfish.

1. Increased permeability of cytoplasmic membranes in Escherichia coli was a consequence of alternative complement pathway (ACP) activity of serum of channel catfish, Ictalurus punctatus. Evidence was provided by beta-galactosidase activity extracellularly when E. coli was incubated with catfish serum. 2. Lesions were detected on outer membranes of E. coli following exposure to catfish serum. 3. Catfish ACP induced a temporal sequence of pre-killing and killing phases. 4. Loss of cell viability, killing rate and cytoplasmic enzyme release increased with increasing serum concentrations. 5. By incubating E. coli with sera treated to remove complement, both release of cytoplasmic enzyme and bactericidal activity were eliminated. 6. Lethal activity associated with channel catfish ACP against Gram-negative bacteria was functionally comparable to that seen in mammalian and reptilian systems.

Animals↗
PubMed1990

Transfusion of ABO-mismatched platelets leads to early platelet refractoriness.

Forty-three consecutive patients previously unexposed to platelets and undergoing treatment for acute leukaemia or autografting for relapsed Hodgkin's lymphoma were randomized to receive transfused platelets of either their own ABO group (OG) or of a major mismatched group (MMG). The 26 evaluable patients were equally distributed between the two study groups. Nine of 13 (69%) MMG patients became refractory with a median onset at transfusion 7 (15 d), compared with only one of 13 (8%) OG patients (P = 0.001). Refractoriness was associated with the formation of high titre isoagglutinins, anti-HLA and platelet specific antibodies. In one patient refractoriness appeared to be due to high titre isoagglutinins alone. Six other patients developed an increase in isoagglutinin titre sufficient to adversely affect platelet increments. Patients receiving ABO-mismatched platelets had a higher incidence of anti-HLA antibodies (5 v. 1) and platelet specific antibodies (4 v. 1). ABO-mismatched platelets transfused prior to the onset of refractoriness resulted in increments similar to those achieved by ABO-matched platelets. The study demonstrates that ABO-mismatched platelets are as effective as matched platelets in patients with low titre isoagglutinins requiring only few transfusions. However, the greater incidence of early refractoriness induced in MMG patients indicates that ABO-mismatched platelets should not be given to patients with marrow failure requiring long-term support.

ABO Blood-Group System↗
PubMed1988

Crystal structure of neutral protease from Bacillus cereus refined at 3.0 A resolution and comparison with the homologous but more thermostable enzyme thermolysin.

Neutral protease from Bacillus cereus exhibits a 73% amino acid sequence homology to thermolysin, for which an accurate crystal structure exists. The B. cereus enzyme is, however, markedly less thermostable. The neutral protease was crystallized and diffraction data to 3.0 A resolution were recorded by oscillation photography. The crystal structure was solved by molecular replacement methods using thermolysin as a trial molecule. The solution was improved by rigid-body refinement and model rebuilding into electron density omit-maps. The atomic co-ordinates were refined to R = 21.7% at 3.0 A resolution. Comparison of the resultant model with the thermolysin structure shows that the two enzymes are very similar with a root-mean-square deviation between equivalent C alpha-atoms of 0.88 A. The gamma-turn found in thermolysin is transformed into a beta-turn in the neutral protease by the insertion of a glycine residue. There appear to be no contributions to the enhanced thermostability of thermolysin from additional salt bridges, whereas contributions in the form of extra hydrogen bonding interactions could be important. Other factors that may affect thermostability include the two glycine to alanine exchanges and perturbations in the environment of the double calcium site.

Amino Acid Sequence↗
PubMed1987

Application of a new method for detecting the phenotype of target binding cells.

A new method was developed for detecting the phenotype of target binding cells (TBC) in a single-cell assay system. This methodology was evaluated during a clinical trial of recombinant interferon alfa-2a (rIFN alfa-2a) for the treatment of 10 metastatic renal cell carcinoma patients. Total TBC with K562 targets, HNK-1+ TBC, and HLA-DR+ TBC were quantitated during rIFN alfa-2a therapy. A significantly increased proportion of lymphocytes bound to target cells on day 9 of therapy bore the HNK-1 marker. This proportion subsequently declined to pretreatment levels. Total TBC paralleled the rise and fall in HNK-1+ TBC. HLA-DR+ TBC binding to targets remained constant and low throughout therapy. These findings suggest that rIFN alfa-2a early in therapy (day 9) caused the recruitment of additional HNK-1+ cells into binders. However, with continued therapy, this proportion reverts to pretreatment levels. The results of this clinical trial served to illustrate the ability of the modified single-cell assay system to detect TBC phenotype.

Antibodies, Monoclonal↗
PubMed1986

Interdonor incompatibility due to anti-Kell antibody undetectable by automated antibody screening.

A unit of whole donor blood, the plasma of which contained anti-Kell antibody, was transfused into a Kell-negative patient who had received a unit of Kell-positive blood 4 weeks previously. A haemolytic transfusion reaction ensued. The antibody had gone undetected in routine automated screening of the donor blood. Automated antibody detection techniques do not offer reliable detection of anti-Kell antibodies.

Blood Group Antigens↗
PubMed1984

Allosteric interactions of glycogen phosphorylase b. A crystallographic study of glucose 6-phosphate and inorganic phosphate binding to di-imidate-cross-linked phosphorylase b.

The binding to glycogen phosphorylase b of glucose 6-phosphate and inorganic phosphate (respectively allosteric inhibitor and substrate/activator of the enzyme) were studied in the crystal at 0.3 nm (3A) resolution. Glucose 6-phosphate binds in the alpha-configuration at a site that is close to the AMP allosteric effector site at the subunit-subunit interface and promotes several conformational changes. The phosphate-binding site of the enzyme for glucose 6-phosphate involves contacts to two cationic residues, Arg-309 and Lys-247. This site is also occupied in the inorganic-phosphate-binding studies and is therefore identified as a high-affinity phosphate-binding site. It is distinct from the weaker phosphate-binding site of the enzyme for AMP, which is 0.27 nm (2.7A) away. The glucose moiety of glucose 6-phosphate and the adenosine moiety of AMP do not overlap. The results provide a structural explanation for the kinetic observations that glucose 6-phosphate inhibition of AMP activation of phosphorylase b is partially competitive and highly co-operative. The results suggest that the transmission of allosteric conformational changes involves an increase in affinity at phosphate-binding sites and relative movements of alpha-helices. In order to study glucose 6-phosphate and phosphate binding it was necessary to cross-link the crystals. The use of dimethyl malondi-imidate as a new cross-linking reagent in protein crystallography is discussed.

Adenosine Monophosphate↗
PubMed1983

The East Baltimore study: the relationship of lipids and lipoproteins to selected cardiovascular risk factors in an inner city Black adult population.

Low socioeconomic status, inner city Black adults, aged 20 to 49 yr (24 males and 45 females), were randomly selected from East Baltimore, MD to study plasma lipid and lipoprotein levels. Several factors known to affect these levels also were examined: dietary intake, alcohol intake, degree of obesity (measured by body mass index), physical activity level, smoking, and hormone use. Compared to women, the men consumed 9.3 more calories/kg body weight (p less than 0.005), 273 mg more cholesterol/day (p less than 0.005), and 7% fewer calories as sucrose (p less than 0.01). The P/S ratio of both their diets was 0.5. The men also had a lower body mass index than the women (23.9 kg/m2 versus 29.0; p less than 0.001). Mean lipid and lipoprotein levels were similar in the men and women. However, the men's total cholesterol (167 mg/dl) and low density lipoprotein cholesterol (94 mg/dl) levels were lower than those of adult Blacks in other studies, while the levels of the East Baltimore women were similar to those in other studies. For women, body mass index and high density lipoprotein cholesterol were negatively correlated (p less than 0.01); triglycerides and oral contraceptive use were positively correlated (p less than 0.01). None of the factors studied explained the relatively low total cholesterol and low density lipoprotein cholesterol levels in these inner city Black adult men.

Adult↗
PubMed1982

Structural investigations of outer membrane proteins from Escherichia coli.

The receptor of phage lambda of Escherichia coli W3110, and matrix porin from E. coli BE have been crystallized. Porin occurs in two crystal forms whose packing arrangements are different, allowing the conclusion that crystal growth occurs from monodisperse protein-detergent complexes. The tetragonal form yields resolution to 2.9 A. The hexagonal form allows conclusive support for the hypothesis that a large fraction of the polypeptide is present in beta-pleated sheet structure with the strands nearly parallel to the normal of the membrane plane.

Bacterial Proteins↗
PubMed1981

Phosphorylase: control and activity.

Recent results from the crystallographic studies on glycogen phosphorylase b at 2 A resolution are reviewed with special reference to other themes of the meeting. The structural similarity of the fold of 150 residues in phosphorylase to the observed in lactate dehydrogenase is discussed and the binding sites for NADH in phosphorylase are described. The binding of the potent inhibitor glucose-1,2-cyclic phosphate to phosphorylase b in the crystal has been studied at 3 A resolution. The results are compared with those previously obtained for glucose-1-phosphate and discussed with reference to proposals for a mechanism of catalysis that involves the essential cofactor pyridoxal phosphate.

Allosteric Regulation↗
PubMed1981

The East Baltimore study. II. Familial aggregation of plasma lipid levels in juveniles in a black inner-city population.

Familial aggregation of plasma lipid levels among 676 black juveniles, aged less than 20 years and residing in 202 households in East Baltimore, Maryland, was assessed by the intraclass correlation coefficient of residuals from sex-specific cubic regressions on age. Significant aggregation of both plasma cholesterol (r = 0.23, p less than 0.005) and plasma triglyceride (r = 0.27, p less than 0.005) levels were found. In addition, no effect on familial aggregation was found for each of several measures of family structure: number of juvenile household members, closeness in age, all children over 9 years of age, or shared surname. Two methods of classifying juvenile household size were compared. An association between classification method and juvenile household size was demonstrated (p less than 0.005) for the distributions of households and of children. The intraclass correlation coefficients for plasma cholesterol and plasma triglyceride for households classified by number of juveniles were higher than the coefficients for the house grouped by the number of juveniles admitted to the study, when compared for each classification number, 2 through 4. Evidence for an effect on familial aggregation of the socioeconomic status was shown by a comparison of intraclass correlation coefficients from households in East Baltimore with those from white and black households from the Columbia Medical Plan which have higher levels of occupation and education. Higher correlations were shown for the groups with higher socioeconomic status, regardless of race.

Adolescent↗