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D Walz

Publications and source records attributed to D Walz.

At least 37 records · Page 2Linked to original sources
PubMed1995

Chemical oscillations arise solely from kinetic nonlinearity and hence can occur near equilibrium.

A minimal kinetic scheme for a system displaying sustained chemical oscillations is presented. The system is isothermal, and all steps in the scheme are kinetically reversible. The oscillations are analyzed and the crucial points elucidated. Both positive and negative feedback, if properly introduced, support oscillations, provided the state responsible for feedback is optimally buffered. It is shown that the requisite nonlinearity is introduced at the kinetic level because of feedback regulation and not, as is usually assumed, by large affinities that introduce nonlinearity at the thermodynamic level. Hence, sustained oscillations may occur near equilibrium.

Biophysical Phenomena↗
PubMed1991

Tissue kallikrein processes small proenkephalin peptides.

Tissue kallikrein may play a role in processing precursor polypeptide hormones. We investigated whether hydrolysis of natural enkephalin precursors, peptide F and bovine adrenal medulla docosapeptide (BAM-22P), by hog pancreatic kallikrein is consistent with this concept. Incubation of peptide F with this tissue kallikrein resulted in the release of Met5-enkephalin and Met5-Lys6-enkephalin. Met5-Lys6-enkephalin was the main peptide released, indicating that the major cleavage site was between two lysine residues. At 37 degrees C and pH 8.5, the KM values for formation of Met5-enkephalin and Met5-Lys6-enkephalin were 129 and 191 microM, respectively. Corresponding kcat values were 0.001 and 0.03 s-1 and kcat/KM ratios were 8 and 1.6.10(2) M-1.s-1, respectively. Cleavage of peptide F at acidic pH (5.5) was negligible. When BAM-22P was used as a substrate, Met5-Arg6-enkephalin was released, thus indicating cleavage between two arginine residues. At pH 8.5, KM was 64 microM, kcat was 4.5 s-1, and the kcat/KM ratio was 7.10(4) M-1.s-1. At 5.5, the pH of the secretory granules, KM, kcat and kcat/KM were 184 microM, 1.9 s-1 and 10(4) M-1.s-1, respectively. It is unlikely that peptide F could be a substrate for kallikrein in vivo; however, tissue kallikrein could aid in processing proenkephalin precursors such as BAM-22P by cleaving Arg-Arg peptide bonds.

Amino Acid Sequence↗
PubMed1991

Inherited platelet-storage pool deficiency associated with a high incidence of acute myeloid leukaemia.

A family with an inherited bleeding disorder extending over four generations, and multiple cases of myeloblastic and myelomonoblastic leukaemia was studied. Ten members of the family had, by history, a haemorrhagic diathesis. There were three documented cases of myeloblastic leukaemia, two documented cases of myelomonoblastic leukaemia and two more cases of leukaemia by history. In four of the cases the bleeding diathesis clearly antedated the leukaemia, in two by many years. The bleeding disorder is characterized by a long bleeding time, abnormal platelet aggregation, low platelet ADP and decreased numbers of platelet dense bodies consistent with a dense granule storage pool deficiency. The number of dense granules was decreased by immunofluorescence employing quinacrine or using an antibody to the dense granule membrane protein, granulophysin, confirming an absolute decrease in dense granule numbers rather than the presence of empty granule sacs. This congenital storage pool deficiency is associated with a high incidence of acute myeloid leukaemia in this family.

Acute Disease↗
PubMed1990

Binding of p-nitrophenyl alpha-D-galactopyranoside to lac permease of Escherichia coli.

Binding of the substrate analogue p-nitrophenyl alpha-D-galactopyranoside (NPG) to lac permease of Escherichia coli in different membrane preparations was investigated. Binding was assayed with an improved version of the centrifugation technique introduced by Kennedy et al. [Kennedy, E.P., Rumley, M.V., Armstrong, J.B. (1974) J. Biol. Chem. 249, 33-37]. Two binding sites for NPG were found with dissociation constants of about 16 microM and 1.6 mM at pH 7.5 and room temperature. With purified lac permease reconstituted into proteoliposomes, it could be shown that one permease molecule binds two substrate molecules. Oxidation of lac permease with the lipophilic quinone plumbagin or alkylation with the sulfhydryl reagent N-ethylmaleimide caused a 12-fold increase in the first dissociation constant. The second dissociation constant seemed to be increased as well, but its value could not reliably be estimated. Ethoxyformylation of lac permease with diethyl pyrocarbonate totally abolished NPG binding. The implications of these results for the catalytic performance of the enzyme are discussed.

Cell Membrane↗
PubMed1989

A new ELISA method for the rapid quantification of Tamm-Horsfall protein in urine.

The authors present a simplified enzyme-linked immunosorbent assay (ELISA) technique for the quantitative measurement of urinary Tamm-Horsfall protein (THP). Microtiter plates are coated with THP and urine samples at various dilutions without the need for a capture antibody. The bound glycoprotein is then incubated with a monoclonal anti-THP antibody and an alkaline phosphatase conjugated anti-IgG antibody. The assay was validated and gave reproducible results over a wide range of absorbance values. The sensitivity of the assay for THP was 2-5 micrograms/L, the coefficient of variation between assays 7.5%, and the day-to-day variability 11.1% for THP concentrations between 6.25 and 200 micrograms/L. THP excretion was assayed in five volunteers over five days comparing THP concentration in spot urines and in 24-hour urine collections.

Adult↗
PubMed1989

The degree of stacking and the average membrane area of thylakoids in lettuce chloroplasts.

The surface density of stacked and total thylakoid membranes in chloroplasts was determined morphometrically using the method of vertical sections. The degree of stacking, defined as the fraction of the total membrane area which is involved in stacking, was calculated from the surface densities and found to be 0.70 for chloroplasts of lettuce grown under field conditions. An average membrane area of 500 microns 2 for the thylakoids in a chloroplast was obtained from the surface density and the average volume of the chloroplasts (11.6 microns 3, estimated by means of equivalent oblate spheroids). The advantage of the morphometric method over alternative techniques and the relevance of the results with respect to the topology of thylakoid membranes are discussed.

Chloroplasts↗
PubMed1988

A new kinin moiety in human plasma kininogens.

Recently, we isolated a new kinin from human urine and tentatively identified it as [Ala3]-Lys-bradykinin. However, there were inconsistencies between the properties of the naturally occurring new kinin and synthetic [Ala3]-Lys-bradykinin. In the present work, we determined whether the new kinin was released from human plasma kininogen, and further investigated the structure of the new kinin. After incubation of plasma (n = 6) with human urinary kallikrein, kinins were separated by HPLC and measured by RIA. The new kinin and Lys-bradykinin were found representing 23 +/- 3 and 76 +/- 6%, respectively, of total kinins released (2.0 +/- 0.4 micrograms/ml). The new kinin was also released from both purified low- and high-molecular-weight kininogens, representing 40-42% of total kinins released. Amino acid sequencing and composition analysis indicated that the structure of the new kinin was [Hyp3]-Lys-bradykinin (Lys-Arg-Pro-Hyp-Gly-Phe-Ser-Pro-Phe-Arg) and not [Ala3]-Lys-bradykinin. We conclude that an important proportion of human kininogens contain hydroxyproline instead of proline in position three of the bradykinin moiety.

Amino Acid Sequence↗
PubMed1988

Circular dichroism of platelet factor 4.

The circular dichroism of platelet factor 4 was investigated and it was found to contain 15% alpha-helix, 25% beta-structure, and the rest of the molecule in unordered conformation. In the presence of heparin, no change in the circular dichroism was observed, suggesting no significant changes in the secondary structure of platelet factor 4 when heparin binds. The CD spectrum of platelet factor 4 was also investigated in the presence of increasing concentrations of guanidine hydrochloride. A two-state transition was observed with midpoints at 0.125 and 2.0 M guanidine hydrochloride. Based on gel filtration studies, the first unfolding transition was correlated with the dissociation of the tetrameric structure. This first unfolding domain was not observed in the presence of heparin, suggesting that heparin stabilizes the tetrameric structure. The second unfolding transition corresponds to the disruption of the overall secondary structure which is generally observed with most proteins. It is concluded that a relatively weak force of attraction holds the tetrameric structure of platelet factor 4 and the dissociation of the subunits is accompanied by loss of some helical secondary structure.

Chromatography, Gel↗
PubMed1988

An evolutionary tree for invertebrate globin sequences.

A phylogenetic tree was constructed from 245 globin amino acid sequences. Of the six plant globins, five represented the Leguminosae and one the Ulmaceae. Among the invertebrate sequences, 7 represented the phylum Annelida, 13 represented Insecta and Crustacea of the phylum Arthropoda, and 6 represented the phylum Mollusca. Of the vertebrate globins, 4 represented the Agnatha and 209 represented the Gnathostomata. A common alignment was achieved for the 245 sequences using the parsimony principle, and a matrix of minimum mutational distances was constructed. The most parsimonious phylogenetic tree, i.e., the one having the lowest number of nucleotide substitutions that cause amino acid replacements, was obtained employing clustering and branch-swapping algorithms. Based on the available fossil record, the earliest split in the ancestral metazoan lineage was placed at 680 million years before present (Myr BP), the origin of vertebrates was placed at 510 Myr BP, and the separation of the Chondrichthyes and the Osteichthyes was placed at 425 Myr BP. Local "molecular clock" calculations were used to date the branch points on the descending branches of the various lineages within the plant and invertebrate portions of the tree. The tree divided the 245 sequences into five distinct clades that corresponded exactly to the five groups plants, annelids, arthropods, molluscs, and vertebrates. Furthermore, the maximum parsimony tree, in contrast to the unweighted pair group and distance Wagner trees, was consistent with the available fossil record and supported the hypotheses that the primitive hemoglobin of metazoans was monomeric and that the multisubunit extracellular hemoglobins found among the Annelida and the Arthropoda represent independently derived states.

Amino Acid Sequence↗
PubMed1988

Isolation and partial characterization of gastrotropin from canine ileum: further studies of the parietal and chief cell response.

Gastrotropin (GT), a protein previously isolated from porcine ileal mucosa, with a molecular mass of 14,054 daltons, was extracted from canine ileum and purified to homogeneity. The canine and porcine peptides had similar relative molecular mass, charge, hydrophobicity, and amino acid compositions. Direct Edman degradation yielded no free amino acids, indicating a blocked NH2-terminus, and a partial sequence determination of the CNBr fragments demonstrated a high degree of homology with porcine GT. Previous studies have indicated that GT is a potent enterooxyntin, and to further characterize these observations we have investigated the actions of both porcine and canine GT on isolated enriched preparations of guinea pig and dog parietal and chief cells. The results of these studies demonstrate that GT is present in more than one species and that the cellular response to porcine and canine GT is identical. The efficacies of canine and porcine GT preparations in stimulating pepsinogen secretion and [14C]aminopyrine uptake were identical and equal to those of cholecystokinin octapeptide (CCK8) and pentagastrin. GT was 100-fold more potent than either of these two major secretagogues. Maximal [14C]aminopyrine accumulation was observed with 10(-8) M GT, with an ED50 of 2 x 10(-9) M compared to pentagastrin, which caused maximal accumulation at 10(-6) M and had an ED50 of 5 x 10(-8) M. Maximal pepsinogen secretion was observed with 10(-7) M GT, with an ED50 of 10(-10) M, compared to 10(-6) M for CCK8, with an ED50 of 10(-8) M. The maximal chief cell response to GT was unaffected by the addition of CCK8 or carbachol, but responded additively with forskolin, indicating that GT uses the same transduction mechanism as CCK8 and carbachol and does not involve the activation of adenylate cyclase. The ED50 values observed with both parietal and chief cells in these studies were close to the basal circulating levels of GT (3.5 x 10(-9) M) in adult pigs. These results clearly demonstrate that GT is a potent component of the enterooxyntin factor identified in studies of the role of the small bowel in the regulation of gastric secretion.

Amino Acid Sequence↗
PubMed1987

Role of platelet membrane in enhancement of tumor cell adhesion to endothelial cell extracellular matrix.

Tumor cell adhesion to subendothelial matrix in the presence of platelets and plasma has been examined in vitro using an entirely homologous system of rat Walker 256 carcinosarcoma cells, matrix laid down by rat aortic endothelial cells and rat platelets and plasma. In the presence of platelets or platelets plus plasma, tumor cell adhesion was significantly enhanced when compared to adhesion in the absence of platelets. In the presence of plasma alone (0.1%), we observed no significant increase in tumor cell adhesion. In order to determine which platelet factors contribute to the enhancement of tumor cell adhesion by platelets, we subjected washed rat platelets to mechanical lysis or thrombin stimulation followed by centrifugation. The membrane fractions and supernatant fractions containing platelet attachment proteins were compared for their abilities to support tumor cell adhesion to subendothelial matrix. Platelet membranes were also recombined with platelet supernatant fractions to determine if platelet attachment proteins or platelet membranes required the presence of the other to enhance tumor cell adhesion. Platelet supernatant fractions which contained release reaction proteins (confirmed by polyacrylamide gel electrophoresis) did not enhance tumor cell adhesion. Purified thrombospondin, fibronectin, beta-thromboglobulin, platelet derived growth factor, and serotonin had no effect on tumor cell adhesion. Platelet membrane containing fractions affected tumor cell adhesion to subendothelial matrix as follows: (a) platelets formed an adhesive bridge between tumor cells and the subendothelial matrix as demonstrated by scanning electron microscopy; (b) intact platelets and thrombin stimulated platelets were the most effective at facilitating tumor cell adhesion; (c) preparations containing partially lysed platelet ghosts were more effective in supporting tumor cell adhesion to subendothelial matrix than were preparations containing completely lysed platelet membrane fragments; (d) recombination of platelet supernatant fractions with mechanically lysed platelets did not enhance their ability to support adhesion; (e) fixed platelets, either alone or in combination with platelet supernatant fractions, failed to enhance adhesion. These data indicate that platelet enhanced tumor cell adhesion appears to be dependent on platelet membrane factors including receptor mobility, rather than intraplatelet components.

Animals↗
PubMed1987

Consequences of detailed balance in a model for sensory adaptation based on ligand-induced receptor modification.

A model for exact sensory adaptation has been published by Segel and co-workers in several papers [e.g., Knox, B. E., Devreotes, P. N., Goldbeter, A. & Segel, L. A. (1986) Proc. Natl. Acad. Sci. USA 83, 2345-2349]. The model comprises a pair of states whose relative probabilities are determined by the binding of a ligand. A second pair of states related by the same ligand binding is accessible as a consequence of either a conformational change or a "covalent modification." By taking proper account of detailed balance, we show that the notion of covalent modification in this context includes three cases, two of which involve dissipation of metabolic energy. The condition for exact adaptation is dependent on metabolite concentrations in all cases of covalent modification. The performance of the model is critically examined on thermodynamic and kinetic grounds.

Adaptation, Physiological↗
PubMed1985

Quantitative assessment of irritation in the mouse skin test.

Intracutaneous injection of aqueous solutions of topically irritant substances into the skin of juvenile mice creates a persisting oedema, the strength of which can be assessed by the number of wrinkles formed on reefing the skin at the site of injection. An algorithm is used to transform the number of wrinkles, recorded just before and 2.5 and 6 hr after the injection, into the intensity of the oedematous reaction. This quantity, which does not depend on subjective assessments graded on an arbitrary scale, is reproducible and has been judged to be relevant to the prediction of irritancy likely to arise from accidental contact of substances with mucous membranes.

Animals↗
PubMed1985

Irritant action due to physico-chemical parameters of test solutions.

The irritant action of various buffer solutions was determined by the mouse skin test. All results for isosmolal solutions differing in initial pH values and buffer capacities could be satisfactorily represented by a general model which could be used to predict the irritancy of solutions with unphysiological pH values in contact with mucous membranes. The results obtained with hyperosmolal solutions are as yet too limited for such a general statement, but it appears that increasing osmolality gradually overrides the effect of the pH value. The relevance of the results to the prediction of irritant potentialities for man has been assessed by comparison with results of rabbit-eye tests carried out by Friedenwald et al. (Archs Ophthal., N.Y. 1944, 31, 279).

Animals↗