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J E Pitts

Publications and source records attributed to J E Pitts.

At least 37 records · Page 2Linked to original sources
PubMed1990

The conformation of deamino-oxytocin: X-ray analysis of the 'dry' and 'wet' forms.

Two crystal structures of (1 beta-mercaptopropionic acid) deamino-oxytocin are reported. The 'dry form' in space group C2 has cell dimensions a = 27.08 +/- 0.03, b = 9.06 +/- 0.01, c = 22.98 +/- 0.02 A, beta = 102.06 +/- 0.03 with one deamino-oxytocin and six water molecules per asymmetric unit. The 'wet form' in space group P2(1) has cell dimensions a = 27.27 +/- 0.02, b = 9.04 +/- 0.01, c = 23.04 +/- 0.02 A, beta = 102.24 +/- 0.02, with two deamino-oxytocin and 13 water molecules per asymmetric unit. A local twofold parallel to the monoclinic axis gives a pseudo C2 packing. Initial phases of the 'dry form' were calculated by the heavy-atom method from the isomorphous and anomalous difference Pattersons and anomalous difference Fouier synthesis. The structure was refined by using restrained least-squares at 1.2 A resolution to a crystallographic R = 0.10. The molecular replacement method yielded the P2(1) structure that was refined with geometric restraints to R less than 0.09, by using all data to 1.09 A resolution. Deamino-oxytocin consists of a cyclic tocin ring formed by six amino acids, closed by a disulphide bridge, S1-S6, and held by two trans-annular hydrogen bonds N2-O5 and N5-O2 with a type II turn at residues 3 and 4. A flexible tripeptide tail has a loosely hydrogen-bonded type I beta-turn between N9 and O6. The sulphur of cysteine at position 1 is disordered in all the molecules leading to alternative hands of disulphide. The conformational flexibility of Ile 3, Asn 5, Pro 7 side chains and the disulphide bridge is consistent with previous models of oxytocin in which flexibility is necessary for biological activity.

Amino Acid Sequence↗
PubMed1990

Variation in the THC content of illicitly imported Cannabis products--1984-1989.

The tetrahydrocannabinol (THC) content of more than 180 samples of fresh illicit Cannabis products, seized by H.M. Customs and Excise on entry into Great Britain and Northern Ireland over the period 1984-1989, has been determined by gas chromatography. The average THC content of herbal cannabis remained high due to good quality cannabis from Jamaica and the USA, but that of cannabis resin was slightly lower. Resin from Morocco has changed significantly in its physical appearance. There was no fresh seizure of cannabis oil in this period.

Cannabis↗
PubMed1989

Protein engineering and design.

Rapid advances in site-directed mutagenesis and total gene synthesis combined with new expression systems in prokaryotic and eukaryotic cells have provided the molecular biologist with tools for modification of existing proteins to improve catalytic activity, stability and selectivity, for construction of chimeric molecules and for synthesis of completely novel molecules that may be endowed with some useful activity. Such protein engineering can be seen as a cycle in which the structures of engineered molecules are studied by X-ray analysis and two-dimensional nuclear magnetic resonance. The results are used in the improvement of the design by using knowledge-based procedures that exploit facts, rules and observations about proteins of known three-dimensional structure.

Amino Acid Sequence↗
PubMed1986

Coypu insulin. Primary structure, conformation and biological properties of a hystricomorph rodent insulin.

Insulin from a hystricomorph rodent, coypu (Myocaster coypus), was isolated and purified to near homogeneity. Like the other insulins that have been characterized in this Suborder of Rodentia, coypu insulin also exhibits a very low (3%) biological potency, relative to pig insulin, on lipogenesis in isolated rat fat-cells. The receptor-binding affinity is significantly higher (5-8%) in rat fat-cells, in rat liver plasma membranes and in pig liver cells, indicating that the efficacy of coypu insulin on receptors is about 2-fold lower than that of pig insulin. The primary structures of the oxidized A- and B-chains were determined, and our sequence analysis confirms a previous report [Smith (1972) Diabetes 21, Suppl. 2, 457-460] that the C-terminus of the A-chain is extended by a single residue (i.e. aspartate-A22), in contrast with most other insulin sequences, which terminate at residue A21. In spite of a large number of amino acid substitutions (relative to mammalian insulins), computer-graphics model-building studies suggest a similar spatial arrangement for coypu insulin to that for pig insulin. The substitution of the zinc-co-ordinating site (B10-His----Gln) along with various substitutions on the intermolecular surfaces involved in the formation of higher aggregates are consistent with the observation that this insulin is predominantly 'monomeric' in nature. The c.d. spectrum of coypu insulin is relatively similar to those of casiragua insulin and of bovine insulin at low concentration.

Amino Acid Sequence↗
PubMed1985

Anisotropic thermal motion and polypeptide secondary structure studied by X-ray analysis at 0.98A resolution.

aPP is a 36-amino acid polypeptide which forms a stable globular structure stabilised by hydrophobic interactions between a polyproline-like helix and an alpha-helix. Crystals contain dimers and are crosslinked by coordination through zinc ions leading to a well-ordered lattice which diffracts X-rays to a resolution of 0.98A. This gives a 5:1 ratio of observations-to-parameters even when anisotropic thermal ellipsoids defined by six parameters for each non-hydrogen atom were refined using least-squares techniques. Rigid body refinement of groups within the polypeptide was also undertaken. The relationship of the principal axes of individual thermal ellipsoids and the librations of rigid side groups to features of secondary, tertiary, and quaternary structures of aPP and its interactions with water molecules are described.

Animals↗
PubMed1984

Conformational studies on the pancreatic polypeptide hormone family.

Pancreatic polypeptide has been extracted and sequenced from a wide range of species. The 36-residue polypeptides have some hormonal characteristics, and show a high degree of sequence homology. Two recently isolated polypeptides, from porcine gut and brain, also show a high degree of sequence homology with the pancreatic polypeptides. It was proposed that these polypeptides were members of a related family. The X-ray determined structure of one member of the family, turkey pancreatic polypeptide, is known to high resolution, but there is no structural information for the others. Studies designed to give an insight into the tertiary structure of these related molecules have been carried out, including model building using interactive computer graphics, circular dichroic spectroscopy and secondary structure prediction using a variety of algorithms. The results indicate that a compact globular conformation, similar to that observed in turkey pancreatic polypeptide may be adopted by all molecules and that this may be more highly conserved than the individual amino acid sequences.

Amino Acid Sequence↗
PubMed1983

Dogfish insulin. Primary structure, conformation and biological properties of an elasmobranchial insulin.

Insulin from an elasmobranch, the spiny dogfish (Squalus acanthias) has been purified to near homogeneity by means of acid-ethanol extraction and salt precipitation. The amino acid sequences of the performic-acid-oxidised A and B chains have been determined and exhibit some unusual features. The A chain contains a total of 22 amino acids; only the insulin from coypu (a member of the Rodentia suborder, Hystricomorpha), has previously been reported to contain an extension past the A21 asparagine. The B10 histidine, which is involved in the formation of the insulin hexamers in higher vertebrates through the co-ordination of zinc, is present in this elasmobranch insulin. Several substitutions relative to bovine insulin occur in the proposed receptor binding region (A5Gln leads to His, B21Glu leads to Pro, B22Arg leads to Lys, B25Phe leads to Tyr). In spite of these substitutions, the maximal response in the rat epididymal fat cell assay is the same for bovine and dogfish insulins; the concentration required to produce the half-maximal response is, however, approximately threefold greater for dogfish insulin than that of bovine insulin. The use of interactive computer graphics model-building predicts that the dogfish insulin can attain a three-dimensional structure very similar to that of bovine insulin; circular dichroic spectra are presented which support the model-building studies.

Adipose Tissue↗
PubMed1983

Adaptation of plasminogen activator sequences to known protease structures.

The sequences of urokinase (UK) and tissue-type plasminogen activator (TPA) were aligned with those of chymotrypsin, trypsin, and elastase according to their 'structurally conserved regions'. In spite of its trypsin-like specificity UK was model-built on the basis of the chymotrypsin structure because of a corresponding disulfide pattern. The extra disulfide bond falls to cysteines 50 and 111d. Insertions can easily be accommodated at the surface. As they occur similarly in both, UK and TPA, a role in plasminogen recognition may be possible. Of the functional positions known to be involved in substrate or inhibitor binding, Asp 97, Lys 143 and Arg 217 (Leu in TPA) may contribute to plasminogen activating specificity. PTI binding may in part be impaired by structural differences at the edge of the binding pocket.

Amino Acid Sequence↗
PubMed1983

The crystal structures of three non-pancreatic human insulins.

X-ray studies on semi-synthetic human insulin have shown that it crystallizes in the rhombohedral space group R3 and is nearly isomorphous with 2 Zn pig insulin. Precession photographs of crystals of human and pig insulins show observable changes in the intensity patterns. Crystallographic analysis and refinement of semi-synthetic human insulin at 1.9 A resolution have shown that its molecular structure is very like that of pig insulin except at the C-terminus of the B chain where the change in sequence occurs. We also report the results of a high resolution crystallographic study of human insulins from different origins. The X-ray diffraction patterns of three non-pancreatic human insulins are indistinguishable from each other and from pancreatic human insulin. Refinement of the structures of the non-pancreatic human insulins has shown that they are identical within the limits of experimental error.

Animals↗
PubMed1981

X-ray analysis (1. 4-A resolution) of avian pancreatic polypeptide: Small globular protein hormone.

The crystal structure of avian pancreatic polypeptide (aPP), a 36-residue polypeptide with some hormonal properties, has been determined by using single isomorphous replacement and anomalous scattering to 2.1-A resolution. The phases were extended to 1.4-A resolution by using a modified tangent formula. The molecule contains two regions of secondary structure-an extended polyproline-like helix (residues 1-8) and an alpha-helix (residues 14-31)-that run roughly antiparallel. The packing together of nonpolar groups from these regions gives the molecule a hydrophobic core in spite of its small size. The aPP molecules form a symmetrical dimer in the crystal stabilized principally by interlocking of nonpolar groups from the alpha-helices. The aPP dimers are crosslinked by coordination of Zn(2+); three aPP molecules contribute ligands to each zinc. The coordination geometry is a distorted trigonal bipyramid. The properties of the aPP molecule in solution are consistent with expectations based on the crystal structure. The aPP molecule has several general features in common with the pancreatic hormones insulin and glucagon. All three hormones have complex mechanisms for self-association. Like insulin, aPP seems to have a stable monomeric structure but its biological activity seems to depend on the more flexible COOH-terminal region analogous to the flexible NH(2)-terminal region of glucagon.

Journal Article↗
PubMed1978

Excretion and biotransformation of carboxymethyl-cysteine in rat, dog, monkey and man.

1. Following an oral dose of S-carboxymethyl [35S]cysteine monkey (rhesus and African green), rat, dog, and man excreted 77,88,95, and 100% respectively of the 35S radioactivity in urine and 7.0, 2.5, 0.7, and 0.3% in faeces during a 3 to 4 day period. 2. The principal drug-related components excreted were unchanged carboxymethylcysteine, dicarboxymethyl sulphide and inorganic sulphate. 3. Rat, dog, and man excreted primarily dicarboxymethyl sulphide and unchanged carboxymethylcysteine and no inorganic sulphate (rat, 7%). 4. Monkey excreted largely inorganic sulphate, moderate amounts of dicarboxymethyl sulphide and a trace of unchanged drug.

Animals↗