PubMed Health⌕ Search

Biomedical subjects

A M de Jong

Publications and source records attributed to A M de Jong.

8 recordsLinked to original sources
PubMed2006

Stability of sitting postures: the influence of degrees of freedom.

Observational studies of sitting have shown that, during spontaneous sitting, people adopt a variety of postures. Various researchers have formulated theories to explain why people adopt their sitting postures. Branton (1969) hypothesized that there is continual need for postural stability while sitting. Dempster (1955) stated that additional stability could be obtained through temporarily closing chains of body segments, or, in other words, through decreasing the number of degrees of freedom of the body. The present study elaborates on Dempster's theory. The aim of this study was to determine the influence of the degrees of freedom of the body on postural stability in sitting postures. For 21 different sitting postures, the total number of degrees of freedom was determined. Postural sway, a measure for postural stability, was determined using a 3D motion and position measurement system with ten healthy subjects. This study shows that the mean path length at the level of the second thoracic vertebra (PL0.05), a measure derived from postural sway, increases significantly (p < 0.0001) with an increase of the number of degrees of freedom of the body (DoFB). Closer examination of the data showed that a model taking into account only the degrees of freedom of the lumbar and thoracic spine and pelvis seems to be a better predictor of postural sway than the total number of degrees of freedom of the body.

Biomechanical Phenomena↗
PubMed2003

Reasons for adopting technological innovations reducing physical workload in bricklaying.

In this paper the adoption of technological innovations to improve the work of bricklayers and bricklayers' assistants is evaluated. Two studies were performed among 323 subjects to determine the adoption of the working methods, the perceived workload, experiences with the working methods, and the reasons for adopting the working methods. Furthermore, a comparison of the results of the studies was made with those of two similar studies in the literature. The results show that more than half of the sector adopted the innovations. The perceived workload was reduced. The employees and employers are satisfied with the working methods and important reasons for adoption were cost/benefit advantages, improvement of work and health, and increase in productivity. Problems preventing the adoption were the use of the working methods at specific sites, for instance in renovation work. The adoption of the new working methods could perhaps have been higher or faster if more attention had been paid to the active participation of bricklayers and bricklayers' assistants during the development of the new working methods and to the use of modern media techniques, such as the Internet and CD/DVD.

Construction Materials↗
PubMed2002

Production of chemically pure gaseous [13N]NH3 pulses for PEP studies using a modified DeVarda reduction.

A fast and reproducible production method for pure gaseous [13N]NH3 pulses has been developed. 13N was produced by irradiation of water with 500 nA of 16 MeV protons via the 16O(p,alpha)13N reaction. A mixture of DeVarda's alloy and NaOH was used to convert the produced nitrate/nitrite to ammonia. Pre-treatment of this mixture with water increased the concentrated production of gaseous [13N]NH3. Separation and further purification of ammonia were performed with GC, leading to 5s pulses (1.1 ml STP) with 3.5 +/- 0.5 MBq [13N]NH3 with a high chemical and radiochemical purity suited for positron emission profiling (PEP).

Journal Article↗
PubMed1994

Energy-induced structural changes in NADH:Q oxidoreductase of the mitochondrial respiratory chain.

The reaction of coupled submitochondrial particles (SMP) with NADH was studied in the absence and presence of the uncoupler gramicidin, both in pre-steady-state and steady-state experiments. It was shown that the formation of ubisemiquinones associated with NADH:Q oxidoreductase is insensitive to uncouplers. It was found, however, that in the absence of gramicidin the ubisemiquinone showed a noticeably faster relaxation than in the presence of this uncoupler. During steady-state oxidation of NADH by coupled submitochondrial particles, the EPR signal of iron-sulphur cluster 2 of complex I, the cluster that is generally believed to be the electron donor for ubiquinone, showed some remarkable changes. Its gz line seemed to disappear from the spectrum, although the gxy line remained clearly present. Detailed EPR analysis indicated that (a component of) the gz line shifted to higher field. The temperature dependence of the EPR signal of cluster 2 was affected as well. In the presence of uncoupler the EPR properties of cluster 2 were indistinguishable from those in particles that showed no intrinsic coupling. These experiments strongly indicate that the coordination of cluster 2 is different in energized and non-energized SMP. The pre-steady-state reaction between these submitochondrial particles and NADH showed that the uncoupler-sensitive changes in both the ubisemiquinone and cluster 2 became effective between 9 ms and 30 ms. Similar changes were observed during succinate-driven reverse electron transfer. This report shows, for the first time, energy-induced structural changes in NADH:Q oxidoreductase.

Electron Spin Resonance Spectroscopy↗
PubMed1992

On the stoichiometry of the iron-sulphur clusters in mitochondrial NADH: ubiquinone oxidoreductase.

The concentration of the iron-sulphur (Fe-S) cluster 1b, present in complex I or soluble high-molecular-mass NADH dehydrogenase, was determined using different methods. It was found that direct double integration of the EPR signal at temperatures higher than 40 K, as is commonly used in this field of research, results in a considerable overestimation of the concentration of cluster 1b. It is demonstrated that this is caused by contributions from the relaxation-broadened signals of the Fe-S clusters 2-4 in the enzyme. The correct way for determining the intensity of the EPR signal of cluster 1b is by comparison with a simulated line shape. It is concluded that the concentration of cluster 1b is half that of cluster 2. This corroborates our proposal based on presteady-state kinetic and inhibitor-titration studies [Van Belzen, R., Van Gaalen, M. C. M., Cuypers, P. A. & Albracht S. P. J. (1990) Biochim. Biophys Acta 1017, 152-159] that the minimal functional unit of mitochondrial NADH:ubiquinone oxidoreductase must be a heterodimer.

Animals↗
PubMed1990

Induction of non-bilayer lipid structures by functional signal peptides.

Using 31P NMR and freeze-fracture electron microscopy we investigated the effect of several synthetic signal peptides on lipid structure in model membranes mimicking the lipid composition of the Escherichia coli inner membrane. It is demonstrated that the signal peptide of the E. coli outer membrane protein PhoE, as well as that of the M13 phage coat protein, strongly promote the formation of non-bilayer lipid structures. This effect appears to be correlated to in vivo translocation efficiency, since a less functional analogue of the PhoE signal peptide was found to be less active in destabilizing the bilayer. It is proposed that signal sequences can induce local changes in lipid structure that are involved in protein translocation across the membrane.

Amino Acid Sequence↗
PubMed1983

Inhibitors of calf-brain enkephalinase A and B.

Enkephalinase A and B isolated from calf-brain striatum have comparable substrate specificity (Km for Leu-enkephalin = 1-3.10(-5) microM) but a quite different affinity for certain inhibitors: phosphate, Secobarbital and Thiorphan are effective inhibitors for Enkephalinase A (IC50 of 2.5 mM, 30 microM and 4 nM respectively), while Enkephalinase B does not react with any of these compounds. Both enzymes are inhibited by 1 mM EDTA and o-phenanthroline indicating the presence of a metal atom in or near their active sites. Although with different abilities, both enzymes recognize dipeptides having at least one hydrophobic amino-acid side chain. The potency of such dipeptides can be used for a description of the active site.

Animals↗