Biomedical subjects

A van Boven

Publications and source records attributed to A van Boven.

6 recordsLinked to original sources

PubMed1994

Catheter sizes for quantitative coronary arteriography.

In quantitative coronary arteriography (QCA), the outer diameter of the contrast catheter is used almost exclusively as the calibration device. Since the true outer diameter of these catheters are smaller than the French sizes listed by the manufacturer, it has been advocated to measure the actual sizes with a precision micrometer. However, this represents a significant effort in the organizations of the QCA Angiographic Core Laboratories and of the participating cardiac catheterization laboratories. In the Dutch REGRESS trial on regression/progression of coronary artery disease, we have measured a total of 2,104 catheters from four different manufacturers. In 2,048 of the 2,104 catheters the variabilities in the measurements were 0.02-0.03 mm, which represents an error of only 1% of the average catheter sizes. In the remaining 56 catheter measurements, the variability was 0.04 mm. From these data we may conclude that from now on the stated mean values can be used for calibration purposes. This has important practical consequences for running clinical trials and QCA Core Laboratory operations.

Calibration↗

PubMed1988

Utilization of dipeptides by Lactococcus lactis ssp. cremoris.

Different strains of Lactococcus lactis ssp. cremoris hydrolyze peptides at different rates while the cell-free extracts of these strains all show the same or much higher rates of hydrolysis. These observations indicate that the uptake of peptides is the rate-limiting step in peptide hydrolysis. Utilization of leucyl-leucine by non-growing cells is competitively inhibited by the structurally related dipeptide alanyl-alanine. After hydrolysis of peptides, the amino acids are released into the medium and only a small fraction is accumulated and/or incorporated. This hydrolysis is independent of the synthesis of proteases indicating that the synthesis of proteases and peptidases are regulated differently. The specific growth rate of L. lactis ssp. cremoris E8 depends upon the amino acid source in the medium. No significant differences have been observed in the intracellular peptidase activities and the rates of peptide uptake between L. lactis ssp. cremoris E8 cells grown in different media, indicating that this growth rate is determined by the availability of amino acids in free amino acids or peptides.

Chromatography, High Pressure Liquid↗

PubMed1988

Purification and Characterization of a Dipeptidase from Streptococcus cremoris Wg2.

A dipeptidase was purified to homogeneity from a crude cell extract of Streptococcus cremoris Wg2 by DEAE-Sephacel column chromatography followed by preparative disc gel electrophoresis. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified enzyme showed a single protein band with a molecular weight of 49,000. The dipeptidase is capable of hydrolyzing a range of dipeptides, but not peptides with longer chains. The enzyme was shown to be a metallo-Mn enzyme with a pH optimum of 8 and a temperature optimum of 50 degrees C. The enzyme is strongly inhibited by thiol-reducing reagents but not by sulfhydryl reagents. Kinetic studies indicated that the enzyme has a relatively low affinity for leucyl-leucine and alanyl-alanine (K(m), 1.6 and 7.9 mM, respectively) but can hydrolyze these substrates at very high rates (V(max), 3,700 and 13,000 mumol/min per mg of protein, respectively).

Journal Article↗

PubMed1987

A Phosphate-Bond-Driven Dipeptide Transport System in Streptococcus cremoris Is Regulated by the Internal pH.

The uptake of amino acids and peptides by Streptococcus cremoris is mediated by different highly specific transport systems. The leucine transport system has a high affinity only for leucine, isoleucine, and valine and no affinity for leucyl-peptides. The transport system for leucyl-leucine is strongly inhibited by several dipeptides with hydrophobic, neutral, N-terminal amino acids but not by leucine. The leucyl-leucine transport system has a high affinity for dipeptides containing beta-methyl groups in the side chain; the C terminus of the dipeptide affects the affinity to a much lower extent. Leucyl-leucine transport in whole cells was studied as a function of the internal pH at different external pH values in the presence and absence of nigericin. The internal pH was shown to be an important controlling factor in leucyl-leucine uptake, but the DeltapH was not involved as a driving force. At increasing external pH values, the affinity of the transport system for leucyl-leucine decreased. Uptake of leucyl-leucine was also studied in the presence of arsenate, which inhibited ATP synthesis by substrate-level phosphorylation. The rate of leucyl-leucine transport appeared to be dependent on the intracellular ATP concentrations. These results indicate that the energy for the leucyl-leucine transport is directly supplied by ATP.

Journal Article↗

PubMed1986

Energetics of Leucyl-Leucine Hydrolysis in Streptococcus cremoris Wg(2).

The hydrolysis of the dipeptide leucyl-leucine by whole cells of Streptococcus cremoris Wg(2) was dependent on the presence of the energy source lactose. Incubation of cells with uncouplers or ATPase inhibitors prevented the increase of peptidase activity upon the addition of lactose. Incubation with the ionophore nigericin resulted in decreased peptide hydrolysis activity, while incubation with valinomycin led to increased hydrolysis activity. In the presence of nigericin the DeltapH component of the proton motive force was decreased, while the electrical potential was increased. With valinomycin, the electrical potential was collapsed and the DeltapH was increased. When the external pH was decreased from 8 to 5, the rate of peptide hydrolyzing activity by whole cells increased with increasing DeltapH component. In contrast, the peptide hydrolyzing activity in the cell extract decreased with decreasing external pH. These results indicate that the DeltapH component of the proton motive force determines the leucyl-leucine hydrolyzing activity in S. cremoris Wg(2).

Journal Article↗

PubMed1984

Genetic manipulation of the restricted facultative methylotroph Hyphomicrobium X by the R-plasmid-mediated introduction of the Escherichia coli pdh genes.

The inability of Hyphomicrobium X to grow on compounds such as pyruvate and succinate is most likely due to the absence of a functional pyruvate dehydrogenase (PDH) complex. Further support for this was sought by studying the effect of the introduction of the Escherichia coli pdh genes in Hyphomicrobium X on the pattern of substrate utilization by the latter organism. These genes were cloned by in vivo techniques using the broad-host range conjugative plasmid RP4::Mucts. Plasmid RP4 derivatives containing pdh genes were selected by their ability to complement a pyruvate dehydrogenase deletion mutant of E. coli, strain JRG746 recA (ace-1pd) delta 18. The plasmids thus obtained could be transferred through an intermediary host (C600 recA), selecting only for an antibiotic resistance coded for by RP4 and back into JRG746 or other E. coli pdh mutants, upon which they still conferred the wild type phenotype. Enzyme assays showed that the latter strains, when carrying plasmid RP4'pdh1 also possessed PDH complex activity. Conjugation between the auxotrophic E. coli JRG746 (RP4'pdh1) strain and Hyphomicrobium X on pyruvate minimal agar gave rise to progeny which, on the basis of its morphology (stalked bacteria), their ability to grow on C1-compounds and to denitrify (now also with pyruvate) were identified as hyphomicrobia. This Hyphomicrobium X transconjugant was also able to grow in minimal medium with succinate, but no other novel growth substrates have been identified so far.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacteria↗