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Biomedical subjects

W C Kenney

Publications and source records attributed to W C Kenney.

At least 37 records · Page 2Linked to original sources
PubMed1992

Multiple peak formation from reversed-phase liquid chromatography of recombinant human platelet-derived growth factor.

Reversed-phase liquid chromatography of recombinant platelet-derived growth factor (PDGF) results in the appearance of at least four distinguishable peaks. The relative areas of these peaks are, in part, dependent upon the gradient time and the temperature. Isolation and reinjection of each peak gave chromatographic profiles comparable to that obtained from unfractionated PDGF. Increasing the temperature above 60 degrees C resulted in a single peak that, when isolated and reinjected at ambient temperature, produced a chromatogram comparable to PDGF which had not been exposed to elevated temperature. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that all four peaks had the same molecular mass as PDGF and were active as determined by a PDGF mitogenic bioassay. These results indicate that multiple conformations of PDGF are present and we postulate that their appearance may be a result of isomeric structures arising from the presence of Pro-Pro bonds within the primary structure of the protein.

Amino Acid Sequence↗
PubMed1991

The secondary structure of two recombinant human growth factors, platelet-derived growth factor and basic fibroblast growth factor, as determined by Fourier-transform infrared spectroscopy.

The secondary structures of two recombinant human growth factors, platelet-derived growth factor and the basic fibroblast growth factor, have been quantitatively examined by using Fourier transform infrared spectroscopy. These studies, carried out in D2O, focus on the conformation-sensitive amide I region. Resolution enhancement techniques, including Fourier self-deconvolution and derivative spectroscopy, were combined with band fitting techniques to quantitate the spectral information from the broad, overlapped amide I band. The results presented here indicate that both proteins are rich in beta-structures. The remainder of the platelet-derived growth factor exists largely as irregular or disordered conformations with a moderate amount of alpha-helix and a small portion of reverse turns. By contrast, the basic fibroblast growth factor is much richer in reverse turn structures and contains a lesser portion of irregularly folded or disordered structures. Based on circular dichroism studies which indicate no alpha-helix in bFGF, components near 1655 cm-1 in the bFGF spectra are tentatively assigned to loops. The results of this study emphasize the need for using a combination of circular dichroism and infrared studies for spectroscopic characterization of protein secondary structure.

Cell Membrane Permeability↗
PubMed1991

Conformational changes of recombinant human granulocyte-colony stimulating factor induced by pH and guanidine hydrochloride.

Fluorescence and circular dichroism were used to follow the pH-dependent conformational changes of granulocyte colony stimulating factor (G-CSF). Tryptophan fluorescence of the spectra monitored at 344 nm, or after deconvolution of the emission spectra, at 345 nm, showed a decrease in intensity on going from pH 7 to 4, with a midtransition pH of 5.8. On the other hand, tyrosine fluorescence measured either by the ratio of intensity at 308 nm to that at 344 nm, or by the fluorescence intensity at 303 nm after deconvolution of the spectra, increased in intensity as the pH was changed from 6 to 2.5, with a midtransition pH of 4.5. Near UV circular dichroic spectra also showed changes between pH 7.5 and 4.5, which correlated with the transition monitored by the tryptophan fluorescence. The guanidine hydrochloride-induced conformational changes of G-CSF at five pH values from 2.5 to 7.5 were also studied. Circular dichroic and fluorescence spectra revealed minor conformational changes by the addition of 1 or 2 M guanidine HCl at all pH values examined, while the major conformational transition occurred between 2 and 4 M guanidine hydrochloride. The secondary structure of the protein was most stable between pH 3.3 and 4.5. The guanidine HCl-induced denaturation of G-CSF involved more than a two-state transition, with detectable intermediate(s) present, and the structure of the intermediate(s) appeared to depend on the pH used. These results are consistent with the pH dependence of the structure described above, and demonstrate the complex conformational properties of G-CSF.

Circular Dichroism↗
PubMed1991

Densimetric determination of carbohydrate content in glycoproteins.

Carbohydrates play important roles in activity, stability and pharmacokinetics of glycoproteins and the degree of glycosylation varies with proteins. In this communication, a simple method of determining the carbohydrate content was developed, which consists of measuring the density increments of a glycoprotein and its non-glycosylated counterpart, and then dividing the difference between the two values by the density increment of carbohydrates. The density increment was relatively constant for various sugars except for sialic acid, and hence assumed to be 0.39. Thus, we obtained carbohydrate contents of 38, 28, 8 and 7% for Chinese hamster ovary cell-expressed erythropoietin (EPO), stem cell factor (SCF), granulocyte-colony-stimulating factor (G-CSF), and platelet-derived growth factor (PDGF), respectively. These values are in close agreement with those determined by other methods.

Animals↗
PubMed1988

Control of misincorporation of de novo synthesized norleucine into recombinant interleukin-2 in E. coli.

Interleukin-2 produced from a recombinant E. coli was found to contain as much as 19% norleucine in place of methionine in a minimal medium fermentation. Medium supplementation experiments and use of a leucine-requiring mutant host strain indicated the origin of norleucine to be de novo biosynthesis by reactions involving the enzymes of the leucine biosynthetic pathway. The misincorporation was highly suppressed by addition of either L-leucine or L-methionine to the fermentation and completely suppressed by adding both amino acids.

Aminocaproates↗
PubMed1988

Identification of unusual replacement of methionine by norleucine in recombinant interleukin-2 produced by E. coli.

Moderate amounts of norleucine incorporation into recombinant interleukin-2 (IL-2) produced in E. coli have been detected. Incorporation of norleucine occurs both at the amino terminal and internal methionines as confirmed by the isolation of norleucine-containing tryptic peptides which eluted later than the respective methionine-containing peptides by reverse-phase HPLC. The occurrence of norleucine in intact protein and modified peptides was determined by amino acid analysis and amino acid sequencing including Edman degradation and fast atom bombardment mass spectrometry. In the subsequent paper, we determined that norleucine incorporation is caused by the endogenous synthesis of norleucine in E. coli.

Amino Acid Sequence↗
PubMed1988

High-performance size-exclusion chromatography of recombinant derived proteins and aggregated species.

The chromatographic behavior of some recombinant derived proteins and aggregated species was studied using high-performance size-exclusion chromatography (HPSEC). At neutral pH values, monomeric proteins exhibited non-ideal behavior while aggregated species were not eluted. As the pH was lowered below 5, both aggregated and monomeric species were eluted, with the amount of aggregated species increasing with decrease in pH. Final elution conditions selected for the simultaneous chromatography of monomeric and aggregated proteins were 0.1 M orthophosphoric acid, pH 2.5. The utility of the system was evaluated by determining the rates of protein degradation at elevated temperatures and comparing the results with those obtained using standard bioassay procedures. The rate of formation of aggregated species was also determined by HPSEC and corresponded to the rate of degradation of monomeric protein. The use of HPSEC with low pH eluent provides a rapid means for estimating protein stability under accelerated temperature conditions as well as for determining the existence and formation of aggregated species.

Chromatography, Gel↗
PubMed1988

Secondary structure of interleukin-2(Ala125) in unfolded state.

Secondary structure of interleukin-2(Ala125) in unfolded state was examined by circular dichroism (CD). Unfolding of tertiary structure of the protein, as determined by CD, was observed when the solvent pH was decreased below 3.0 or the disulfide bond was reduced. Consistent with the CD results, a stronger fluorescence enhancement of 1-anilinonaphthalene-8-sulfonic acid was observed on acidification or reduction of interleukin-2(Ala125) relative to that of the native protein, indicating a larger hydrophobic surface exposed to solvent. However, the secondary structure was fully retained in 5% acetic acid or aqueous HCl, pH 3.0. It seemed that alpha-helical content of the protein is even greater at pH 2.0. Reduced protein showed a far u.v. CD spectrum indistinguishable from the oxidized one at pH 4.0. These results suggest that the secondary structure of interleukin-2(Ala125) does not require tertiary structure.

Circular Dichroism↗
PubMed1987

Three-dimensional structure of interleukin-2.

Interleukin-2 is an effector protein that participates in modulating the immune response; it has become a focal point for the study of lymphokine structure and function. The three-dimensional structure of the interleukin molecule has been solved to 3.0 angstrom resolution. Interleukin-2 has a novel alpha-helical tertiary structure that suggests one portion of the molecule forms a structural scaffold, which underlies the receptor binding facets of the molecule.

Animals↗
PubMed1987

Crystals and a low resolution structure of interleukin-2.

Recombinant derived human interleukin-2 and an analog in which cysteine 125 has been replaced with alanine have been crystallized in a form suitable for x-ray diffraction. The crystals are triclinic, space group P1, with two protein molecules in the unit cell; unit cell parameters are a = 55.8 A, b = 40.1 A, c = 33.7 A, alpha = 90.0 degrees, beta = 109.3 degrees, gamma = 93.2 degrees. The interleukin-2 structure has been solved to 5.5 A resolution using heavy atom isomorphous replacement methods. The resultant low resolution model reveals a significant fraction of alpha helical secondary structure and outlines the overall tertiary structure of the molecule.

Crystallization↗
PubMed1986

Structure of unfolded and refolded recombinant derived [Ala125]interleukin 2.

Naturally occurring interleukin 2 (IL-2) contains an odd number (three) of cysteinyl residues and thus is susceptible to the formation of a variety of intramolecular and intermolecular disulfide bonds. The cysteine at residue 125 has been replaced with an alanine residue by site-directed mutagenesis, and hence, this analogue can form only one intrachain disulfide bond. When expressed at high levels in Escherichia coli, this recombinant DNA derived IL-2 analogue is insoluble, reduced, and inactive. The protein was solubilized by denaturants and, after purification, was oxidized to form an intramolecular disulfide bond. Circular dichroism (CD) has been used to investigate the effects of various denaturants on the unfolding-refolding process of the purified, oxidized protein. A similar conformation is obtained when [Ala125]interleukin 2 [IL-2(Ala-125)] is refolded from 6 M guanidine hydrochloride, 8 M urea, or 5% acetic acid. The resultant protein, refolded from these denaturants, is monomeric and has activity comparable to or greater than that reported for naturally derived IL-2. In addition to this form, aggregates, as evidenced from gel filtration, are obtained. The specific activities of these are greatly reduced, and CD spectra indicated that they have much less helical content than the monomeric form of the protein. CD spectra also showed that the tertiary structure of IL-2(Ala-125) is entirely different in the presence of sodium dodecyl sulfate (SDS) from that of the monomeric form in the absence of SDS.

Acetates↗
PubMed1986

Parameters for the evaluation of IL-2 stability.

Recombinant DNA derived interleukin-2 stability in accelerated and long term studies was evaluated using biological and protein chemical methods. Various biophysical parameters were investigated for their correlation with bioassay results and for their accuracy and utility as quantitative indicators of change. Biochemically distinguishable forms of the molecule exhibited different levels of IL-2 activity in vitro. Of the methods evaluated, SDS-PAGE and, to a greater extent, reverse phase and TSK based HPLC analyses have been found to measure relevant changes in the structure of human interleukin-2. Those test systems detect covalent and non-covalent aggregates, degradation products, and inappropriately oxidized forms of human interleukin-2 all of which contribute to an overall loss of IL-2 biological activity. Such measures provide sensitive and reproducible indications of changes relative to the standard bioassay. These studies have led to the development of an analog of interleukin-2 which is biologically active and shows improved long term stability.

Biological Assay↗
PubMed1985

Acidic glutathione S-transferases of rat testis.

In most organs of the rat the predominant forms of glutathione S-transferase have alkaline (greater than 7.0) pI values. In contrast, in the cytosol from rat testes almost 50% of the transferase activity is due to isoenzymes with acidic (less than 7.0) pI values. We have purified three acidic forms of glutathione S-transferase from rat testis cytosol. One form accounted for more than 90% of the enzymic activity in the acidic fraction. This major form was a homodimer of a new subunit, termed Yt. This subunit had an electrophoretic mobility that was different from the subunits that form the alkaline transferases. In addition, functional and immunological studies were consistent with the unique nature of the Yt subunit. The two minor acidic enzymes of rat testis appeared to be heterodimers of the Yt subunit and a subunit with an electrophoretic mobility identical with that of the Yb subunit present in some alkaline enzymes.

Amino Acids↗
PubMed1983

Structural, functional and hybridization studies of the glutathione S-transferases of rat liver.

We have purified five forms of glutathione S-transferase from rat liver. One form was the glutathione S-transferase B (ligandin), which is composed of two non-identical subunits with molecular weights of 22,000 (Ya) and 25,000 (Yc). Two of the other transferases were Ya and Yc homodimers. The other two transferases were also homodimers, but their subunit, Yb, had a molecular weight of 24,000. The three proteins containing either Ya or Yc subunits had similar substrate specificities, and all three contained peroxidase activity. The greatest peroxidase activity was present in proteins containing the Yc subunit. Enzymes composed of Yb subunits had minimal peroxidase activity in addition to different substrate specificities. The Ya and Yc containing enzymes bound the ligands bilirubin, and indocyanine green with high affinity (KD less than 5 microM), although the KD values of the YcYc protein were consistently 4- to 12-fold greater than those of the other two transferases. Studies were performed to define the origins of the various isozymes. There was no evidence for conversion of Yc to either Ya or Yb during storage or under conditions favorable to proteolysis. Hybridization studies were performed under denaturing conditions (6 M guanidine-HCl), and a YaYc hybrid was formed from the YaYa and YcYc proteins. In addition, both YaYa and YcYc hybrids were formed from transferase B. The hybrids were functionally similar to the proteins isolated originally from the liver. Attempts to form a YaYb hybrid from the YbYb and YaYa transferases were unsuccessful. This result is consistent with the lack of this enzyme form in the liver. Glutathione S-transferase B and the Ya and Yc homodimers appeared to be hybrids of common subunits. These three transferases had very similar functional and structural characteristics and differed from the transferases that are composed of Yb subunits.

Animals↗
PubMed1983

Evidence for an active site arginine in UDP-glucuronyltransferase.

2,3-Butanedione inactivates the pure form of UDP-glucuronyltransferase used in these experiments (GT2P) (EC 2.4.1.17) purified from pig liver microsomes. The kinetics of the reaction indicates that 2,3-butanedione reacts with two amino acids that affect activity. A rapid, partial inactivation is followed by a slower rate of inactivation that leads eventually to completely inactive enzyme. UDP-glucuronic acid and glucuronic acid, as compared with UDP, are effective as protectors against the slow, secondary phase of inactivation; no ligand tested protected against the rapid phase of inactivation. The lipid environment of GT2P was a determinant of the pseudo-first order rate constant for the slow phase of inactivation, but did not affect the rate of the rapid phase of inactivation. The data suggest that GT2P contains an active site arginine that interacts with the -COO- at C-6 of the glucuronic acid moiety of UDP-glucuronic acid.

Amino Acids↗
PubMed1982

Acetaldehyde adducts of phospholipids.

Incubation of rat liver microsomes with acetaldehyde followed by reduction with borohydride of the Schiff bases formed leads to the formation of the N-ethyl derivatives of phosphatidylethanolamine and phosphatidylserine. Proof for this structure came from a comparison of these microsomal derivatives, and the nitrogenous bases derived therefrom by acid hydrolyses, with synthetic N-ethylphosphatidylethanolamine, N-ethylphosphatidylserine, N-ethylethanolamine, and N-ethylserine. Modification of membrane phospholipids by covalent binding of acetaldehyde to form Schiff bases may perturb some of the biochemical processes associated with membranes.

Acetaldehyde↗