PubMed Health⌕ Search

Biomedical subjects

H Muirhead

Publications and source records attributed to H Muirhead.

At least 37 records · Page 2Linked to original sources
PubMed1989

Preliminary crystallographic studies on duck ovotransferrin.

Crystals of duck ovotransferrin and duck apo-ovotransferrin have been grown from polyethylene glycol solutions. For both crystals, the space group is P2(1)2(1)2(1), the unit cell dimensions for the ovotransferrin are a = 49.6 A, b = 85.6 A, c = 178.7 A and for the apo-ovotransferrin a = 77.6 A, b = 98.8 A, c = 127.0 A, giving four molecules in the unit cell.

Animals↗
PubMed1988

Crystallization of a ternary complex of lactate dehydrogenase from Bacillus stearothermophilus.

Bacillus stearothermophilus lactate dehydrogenase was purified from an overexpressing Escherichia coli cell line. The enzyme has been crystallized in several different forms. All of these crystal forms were grown in the presence of NADH, sodium oxamate and fructose 1,6-bisphosphate. Three crystal forms have been characterized, an orthorhombic P2(1)2(1)2 (type III, a = 86 A, b = 105 A, c = 136 A) and two monoclinic P21 forms (type IV, a = 85 A, b = 118 A, c = 136 A, beta = 96 degrees; type V, a = 112 A, b = 85 A, c = 136 A, beta = 91 degrees). Precession photographs from these crystal forms are very alike, suggesting the molecular packing to be similar in all three forms. The P21 type IV crystals diffract to beyond 2 A spacing and are stable to irradiation with X-rays. A complete medium-resolution (4.7 A) dataset has been collected from a single crystal using synchrotron radiation. Rotation function studies with these data show the two tetramers of the asymmetric unit to be in very similar orientations. Higher-resolution data are being collected.

Cell Line↗
PubMed1988

A specific, highly active malate dehydrogenase by redesign of a lactate dehydrogenase framework.

Three variations to the structure of the nicotinamide adenine dinucleotide (NAD)-dependent L-lactate dehydrogenase from Bacillus stearothermophilus were made to try to change the substrate specificity from lactate to malate: Asp197----Asn, Thr246----Gly, and Gln102----Arg). Each modification shifts the specificity from lactate to malate, although only the last (Gln102----Arg) provides an effective and highly specific catalyst for the new substrate. This synthetic enzyme has a ratio of catalytic rate (kcat) to Michaelis constant (Km) for oxaloacetate of 4.2 x 10(6)M-1 s-1, equal to that of native lactate dehydrogenase for its natural substrate, pyruvate, and a maximum velocity (250 s-1), which is double that reported for a natural malate dehydrogenase from B. stearothermophilus.

Binding Sites↗
PubMed1987

The engineering of a more thermally stable lactate dehydrogenase by reduction of the area of a water-accessible hydrophobic surface.

A site-directed mutant of Bacillus stearothermophilus lactate dehydrogenase (lactate:NAD+ oxidoreductase, EC 1.1.1.27) has been engineered in which the conserved hydrophobic residue isoleucine-250 has been replaced by the more hydrophilic residue asparagine. This isoleucine forms a large part of a water-accessible, hydrophobic surface in the active site of the apo-enzyme which is covered by the B-face of the nicotinamide ring when coenzymes are bound. Reduction in the area of this hydrophobic surface results in the mutant tetramer being more thermally stable than the wild-type enzyme.

Binding Sites↗
PubMed1986

The structure of cat muscle pyruvate kinase.

The complete amino acid sequence of cat muscle pyruvate kinase has been determined and fitted to the 2.6 A resolution electron density map. Residues in the active site region are highly conserved in the cat muscle, chicken muscle, rat liver and yeast enzymes. The enzyme-bound magnesium, which is essential for activity, interacts with the side chain of glutamate-271 and with two main carbonyl groups. Lysine-269 is the probable acid/base catalyst responsible for the interconversion of pyruvate and enolpyruvate. A possible binding site for the essential monovalent cation is proposed.

Amino Acid Sequence↗
PubMed1983

A comparison of the structure and activity of cat and trout muscle pyruvate kinases.

Pyruvate kinase was purified from cat and trout muscle. The enzymes had similar amino acid compositions and subunit molecular weights. In contrast to the mammalian enzyme, the trout muscle pyruvate kinase was activated by fructose 1,6-bisphosphate. However, unlike the L-type pyruvate kinase from mammalian liver it was not phosphorylated by cyclic-AMP-dependent protein kinase. The purified enzyme from cat muscle was carboxymethylated with iodo[2-14C]acetic acid under conditions that led to the preferential labelling of one especially reactive thiol group. The labelled enzyme was cleaved with CNBr, and the radioactive fragment purified. Amino acid sequence analysis of the reactive-thiol-containing fragment from cat muscle pyruvate kinase showed it had the following sequence: Ile-Gly-Arg-[14C]CmCys-Asn-Arg-Ala-Gly-Lys-Pro-Val-Ile-CmCys-Ala-Thr-Gln- Hse. The corresponding peptide from trout pyruvate kinase had only one difference in its amino acid composition and the sequence around the reactive thiol was identical.

Amino Acids↗
PubMed1981

Glucose-6-phosphate isomerase.

Glucose-6-phosphate isomerase (EC 5.3.1.9) is a dimeric enzyme of molecular mass 132000 which catalyses the interconversion of D-glucose-6-phosphate and D-fructose-6-phosphate. The crystal structure of the enzyme from pig muscle has been determined at a nominal resolution of 2.6 A. The structure is of the alpha/beta type. Each subunit consists of two domains and the active site is in both the domain interface and the subunit interface (P.J. Shaw & H. Muirhead (1976), FEBS Lett. 65, 50-55). Each subunit contains 13 methionine residues so that cyanogen bromide cleavage will produce 14 fragments, most of which have been identified and at least partly purified. Sequence information is given for about one-third of the molecule from 5 cyanogen bromide fragments. One of the sequences includes a modified lysine residue. Modification of this residue leads to a parallel loss of enzymatic activity. A tentative fit of two of the peptides to the electron density map has been made. It seems possible that glucose-6-phosphate isomerase, triose phosphate isomerase and pyruvate kinase all contain a histidine and a glutamate residue at the active site.

Amino Acid Sequence↗
PubMed1978

Structure of pyruvate kinase and similarities with other enzymes: possible implications for protein taxonomy and evolution.

The structure determination of pyruvate kinase shows that each subunit of the tetrameric molecule consists of three domains. The largest of these domains has a remarkable similarity to the structure of triosephosphate isomerase. Another domain shows similarities to many other nucleotide binding proteins. We discuss these similarities and their implications for current arguments on protein taxonomy and evolution.

Animals↗