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A Groen

Publications and source records attributed to A Groen.

At least 19 recordsLinked to original sources
PubMed2005

Roles of polymerization dynamics, opposed motors, and a tensile element in governing the length of Xenopus extract meiotic spindles.

Metaphase spindles assemble to a steady state in length by mechanisms that involve microtubule dynamics and motor proteins, but they are incompletely understood. We found that Xenopus extract spindles recapitulate the length of egg meiosis II spindles, by using mechanisms intrinsic to the spindle. To probe these mechanisms, we perturbed microtubule polymerization dynamics and opposed motor proteins and measured effects on spindle morphology and dynamics. Microtubules were stabilized by hexylene glycol and inhibition of the catastrophe factor mitotic centromere-associated kinesin (MCAK) (a kinesin 13, previously called XKCM) and destabilized by depolymerizing drugs. The opposed motors Eg5 and dynein were inhibited separately and together. Our results are consistent with important roles for polymerization dynamics in regulating spindle length, and for opposed motors in regulating the relative stability of bipolar versus monopolar organization. The response to microtubule destabilization suggests that an unidentified tensile element acts in parallel with these conventional factors, generating spindle shortening force.

Adenylyl Imidodiphosphate↗
PubMed2004

Bipolarization and poleward flux correlate during Xenopus extract spindle assembly.

We investigated the mechanism by which meiotic spindles become bipolar and the correlation between bipolarity and poleward flux, using Xenopus egg extracts. By speckle microscopy and computational alignment, we find that monopolar sperm asters do not show evidence for flux, partially contradicting previous work. We account for the discrepancy by describing spontaneous bipolarization of sperm asters that was missed previously. During spontaneous bipolarization, onset of flux correlated with onset of bipolarity, implying that antiparallel microtubule organization may be required for flux. Using a probe for TPX2 in addition to tubulin, we describe two pathways that lead to spontaneous bipolarization, new pole assembly near chromatin, and pole splitting. By inhibiting the Ran pathway with excess importin-alpha, we establish a role for chromatin-derived, antiparallel overlap bundles in generating the sliding force for flux, and we examine these bundles by electron microscopy. Our results highlight the importance of two processes, chromatin-initiated microtubule nucleation, and sliding forces generated between antiparallel microtubules, in self-organization of spindle bipolarity and poleward flux.

Animals↗
PubMed2001

Advantages of long observation in episode-oriented electronic patient records in family practice.

From 1985-2000, 58 Dutch family physicians (FPs) of the Transition Project collected ICPC-coded data on 47, 2451 episodes of care, first in paper records for direct encounters only, later with a complete electronic patient record (EPR) for all (direct and indirect) encounters. Based on these data, the effects of a long observation period and the inclusion of all encounters (both direct and indirect) in the EPR were studied. Long observation periods in EPRs appear to have important advantages for patient documentation and the assessment of the content of family practice. Comparison of data from a one-year versus a four-year observation period showed a shift in utilization rates. In a long observation period, visiting patients appeared to make less demand on care, while the content of the FP's care for selected chronic diseases was reflected more realistically. The inclusion of all indirect encounters in an EPR (as compared to the previous inclusion of direct encounters only) resulted in more than twice the number of coded entries per listed patient, and thus led to a major shift in perspective on the FP's involvement in patient care.

Adolescent↗
PubMed1997

APF/CBP, the small, amphipathic, anionic protein(s) in bile and gallstones, consists of lipid-binding and calcium-binding forms.

Two very similar small anionic, amphipathic proteins, a phospholipid-binding apoprotein (anionic polypeptide fraction [APF]) and a calcium-binding polypeptide (CBP), are found abundantly in bile and all types of gallstones. The often disparate properties among various preparations of APF/CBP could reflect different sources and separation procedures, leading to partly degraded and/or denatured protein and varied association of bile salts, lipids, bile pigments, and detergents. The present study presents new methods for isolation and purification of APF/CBP, and characterizes the preparations thus obtained. It was found that isolation by selective precipitation of proteins from fresh T-tube bile by added calcium chloride, followed by demineralization with ethylenediaminetetraacetic acid (EDTA), removal of salts, lipids, and some pigment by Sephadex LH-20, and serial ultrafiltration yields the purest preparations. Though free of lipids, bile salts, detergents, and most pigments, these new preparations all show the same 7-kd and 12-kd bands on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), the same major peaks on hydrophobic high-performance liquid chromatography (HPLC), and retain the self-associative, lipid- and calcium-binding functions, typical of older preparations obtained by potentially denaturative procedures. The varied properties among APF/CBP preparations are thus apparently related mainly to their content of different proportions of two major components, lipid-binding APF and calcium-binding CBP. Immunologic cross-reactions indicate common epitopes, and amino acid analyses are also similar, suggesting that APF and CBP may have the same polypeptide backbone, but differ because of posttranslational modification(s). Sufficiently pure APF and CBP have now been obtained to permit possible structural identification by sequencing and molecular biological techniques, though such attempts have thus far been unsuccessful.

Apoproteins↗
PubMed1981

Determination of N tau-methylhistamine in plasma and urine by isotope dilution mass fragmentography.

The determination in N tau-methylhistamine by gas chromatography-mass spectrometry is described using bis-heptafluorobutyryl derivatives and deuterium labelled N tau-methylhistamine as internal standard. A description of the synthesis of the internal standard, N tau-trideuteromethylhistamine, is given. Normal concentrations for plasma were 1.4 +/- 0.4 microgram/l (mean +/- 1 S.D., n = 10). The normal values for urine ranged from 60 to 280 microgram/24 h (n = 20). Five asthmatic patients showed above-normal plasma concentrations.

Asthma↗
PubMed1980

Mass fragmentographic analysis of total cholesterol in serum using a heptadeuterated internal standard.

A mass fragmentographic method for the determination of total cholesterol in serum using heptadeuterated [25,26,26,26,27,27,27-2H]cholesterol as internal standard is presented. The results obtained are compared with a colorimetric and gas chromatographic method which were previously proposed as reference methods. Criteria for the development of absolute measurement by means of mass fragmentography and stable isotopically labelled internal standards are given. The conclusion is drawn that, at present, mass fragmentographic methods for the determination of total cholesterol in serum do not fulfil the criteria required for absolute methods.

Adult↗
PubMed1979

Genetically determined electrophoretic variants of the major urinary protein (Mup) complex in mouse urine.

The major urinary protein (Mup-complex) excreted in mouse urine, has been studied electrophoretically both on starch gel and on cellogel. On stargel six anodally migrating protein bands were observed. These bands are designated component 3, 2', 1, and 4 (i.e. two bands) in the order of decreasing mobility toward the anode. The slower protein band of component 4 on starch gel was not observed on cellogel. By testing mouse inbred strains, we were able to dinstinguish five male and four female Mup phenotypes. Test crosses suggested a four-allelic (a, b, c, d,) variation with regard to components 2', 2 and 1: 'group A' strains showed component 1, 'group B' strains components 1 and 2, 'group C' and 'group F' strains none, and 'group D' strains showed components 1 and 2'. Component 3 may be encoded by another Mup locus, although no crossing-over has been observed: presence (A, B, D, and F strains), absence (C strains). Insufficiently reproducible demonstration of the variation with regard to component 4, forced us to exclude this component for strain distinction. The Mup phenotypes described, can be useful for the detection of certain strain contaminations, especially if F1 hybrid Mup phenotypes are distinguishable.

Alleles↗
PubMed1979

Genic heterogeneity and genetic monitoring of mouse outbred stocks.

An outbred stock of Swiss:SE mice has been surveyed for genic heterogeneity at 12 loci, encoding biochemical polymorphisms in mice. Using horizontal starch-gel electrophoresis, 6 loci (Es-1, Es-2, Es-3, Es-5, Trf, Dip-1) revealed no genic heterogeneity within the total sample of 289 male mice examined. The other 6 loci (Mpi-1, Mup-1, Hbb, Gpi-1, Pgm-1, Ldr-1) each showed a 2-allelic variation within each of the 3 stock units (pavillions) involved. A pavillion effect on the observed genotype numbers was found for Pgm-1 and Gpi-1 (P less than 0.10). Inadequate genotyping may have occurred at Gpi-1 and Ldr-1, as suggested by a 'week effect' on the observed genotype numbers (P less than 0.05). For studying long-term genetic changes within outbred stocks, a routine monitoring procedure using biochemical polymorphisms is recommended.

Alleles↗
PubMed1979

Urinary excretion of conjugated homovanillic acid, 3,4-dihydroxyphenylacetic acid, p-hydroxyphenylacetic acid, and vanillic acid by persons on their usual diet and patients with neuroblastoma.

We report quantitative data on beta-glucuronidase- and sulfatase-hydrolyzable conjugates of homovanillic acid, 3,4-dihydroxyphenylacetic acid, p-hydroxyphenylacetic acid, and vanillic acid in the urine of 20 apparently normal and healthy control persons and of three patients with neuroblastoma. We used organic solvent extraction and capillary gas chromatography. There was considerable person-to-person variation in the conjugation percentages calculated. Mean conjugated percentages of the four compounds for 16 normal healthy persons 2.5--40 years of age were, respectively, 12%, 33%, 14%, and 35%. For newborns and patients with neuroblastoma, these percentages were somewhat different. Increased amounts of vanillic acid were found in the urine of the patients with neuroblastoma, but results of a small metabolic study in rats suggest that this increase most probably is of dietary origin.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1978

Evaluation of the enzymatic ammonia method for urine on the Du Pont automatic clinical analyzer.

The enzymatic method for ammonia with the Du Pont Automatic Clinical Analyzer was tested in our laboratory. The method is very suitable for urine samples although the method was released by Du Pont only for plasma samples. The results correlated well with those obtained by a method based on the Berthelot indophenol reaction and by a method based on the use of an ammonium electrode, which has an ammonium ion selective membrane. The day-to-day coefficient of variation is about 2 and 4% at concentration levels of 100 and 50 mumol/1 respectively. The measured and relative ammonia concentration are linearly related. Recovery of added known amounts of ammonium is complete and no interference from glucose, urea, creatinine and uric acid could be demonstrated. Recommendations are given for handling blood and urine samples before analysis.

Ammonia↗
PubMed1977

Pretreatment methods prior to gaschromatographic analysis of volatile fatty acids from faecal samples.

Vacuum distillation and steam distillation have been compared as pretreatment methods prior to the GC analysis of volatile fatty acids (VFA) in faecal material. Vacuum distillation resulted in a recovery range of 90-110% for all VFA in standard solutions. This was superior to the recovery ranges found after pretreatment by steam distillation. Coefficients of variance for steam distilled samples were higher than for vacuum distilled samples. Using a faecal homogenate, the vacuum distillation method was found to be highly reproducible. Spiking experiments substantiated the quantitative recovery of VFA from vacuum distilled samples. Modifications of the standard vacuum distillation procedure showed that care must be taken to ensure adequate cooling of the receiver tube.

Analysis of Variance↗
PubMed1977

The determination of total cholesterol in serum by gas-liquid chromatography compared with two other methods.

A gas-liquid chromatographic method is described for the measurement of total cholesterol in serum. The method has been found to be simple, specific and precise. The results have been compared with the results of the enzymatic method of Röschlau, P., Bernt, E. and Gruber, W. (1974) (Z. Klin. Chem. Klin. Biochem. 12, 403) and with the results of an Auto-Analyzer method based on the manual method of Huang, T.C., Chen, C.P., Wefler, V. and Raftery, A. (1961) (Anal. Chem. 33, 1405) and Ness, A.T., Pastewka, J.V. and Peacock, A.C. (1964) (Clin. Chim. Acta 10, 229). The results of the gas-liquid chromatographic and of the enzymatic method show a high degree of correlation. The results of the Auto-Analyzer method are about 0.75 mmol/1 higher than those of the other two methods. The conclusion is drawn that the gas-liquid chromatographic method should be given consideration as a reference method for the measurement of total cholesterol in serum. It is a viable alternative for the generally accepted colorimetric reference method of Abell, L.L., Levy, B.B., Brodie, B.B. and Kendall, F.E. (1952) (J. Biol. Chem. 195, 357).

Autoanalysis↗
PubMed1977

Identification and genetic monitoring of mouse inbred strains using biochemical polymorphisms.

53 inbred strains and substrains of mice from 3 institutes in The Netherlands were examined at 12 chromosome loci coding body protein-polymorphism Es-1, Es-2, Es-3, Es-5, Gpi-1, Hbb, Id-1, Ldr-1, Mpi-1, Mup-1, Pgm-1, Trf). The allelic variation at 7 loci could be detected simultaneously. Within each institute most strains showed a unique combination of alleles at the 12 loci involved. Some nominally similar (sub)strains showed allelic divergence. One strain showed allelic variation at 4 loci. These findings emphasize the possibility and the necessity of monitoring the genetic purity of inbred strains of mice. A routine monitoring scheme using body protein-polymorphisms is proposed.

Alleles↗