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Biomedical subjects

A Kuipers

Publications and source records attributed to A Kuipers.

8 recordsLinked to original sources
PubMed2000

A truncated soluble Bacillus signal peptidase produced in Escherichia coli is subject to self-cleavage at its active site.

Soluble forms of Bacillus signal peptidases which lack their unique amino-terminal membrane anchor are prone to degradation, which precludes their high-level production in the cytoplasm of Escherichia coli. Here, we show that the degradation of soluble forms of the Bacillus signal peptidase SipS is largely due to self-cleavage. First, catalytically inactive soluble forms of this signal peptidase were not prone to degradation; in fact, these mutant proteins were produced at very high levels in E. coli. Second, the purified active soluble form of SipS displayed self-cleavage in vitro. Third, as determined by N-terminal sequencing, at least one of the sites of self-cleavage (between Ser15 and Met16 of the truncated enzyme) strongly resembles a typical signal peptidase cleavage site. Self-cleavage at the latter position results in complete inactivation of the enzyme, as Ser15 forms a catalytic dyad with Lys55. Ironically, self-cleavage between Ser15 and Met16 cannot be prevented by mutagenesis of Gly13 and Ser15, which conform to the -1, -3 rule for signal peptidase recognition, because these residues are critical for signal peptidase activity.

Amino Acid Sequence↗
PubMed1999

An approach to nutrient management on dairy farms.

In the European Union, groundwater should contain less than 50 mg of nitrate/L. Individual countries have developed alternative strategies for phosphorus (P). In The Netherlands, regulations based on P limited the amount of manure applied per hectare. A more balanced P supply to the land has been achieved by transport of manure from surplus to deficit regions. Costs of processing of manure to pellets appeared to be (too) high. In animal production experiments, lowering the P content of concentrates and mineral supplements reduced P losses without an adverse effect on production. In addition to the European guideline for nitrate, ammonia volatilization should be reduced by 50 to 70%. Management practices for reducing nitrogen (N) losses were studied with a farm model, developed at PR. A combination of a more efficient use of fertilizer N, restricted grazing, and a more balanced diet, and, to a lesser extent, higher milk production per cow resulted in considerable reductions in nitrate leaching. The application of slurry by injection diminishes the ammonia volatilization at farm level by almost 50%. This technique has become obligatory, and is only allowed during the growing season. Other techniques, like low emission housing and covering of slurry storage have relatively high costs. Starting in 1998, farmers have to keep a record of nutrients on a balance sheet. A tax will be imposed on surpluses of N and P. This new instrument replaces the regulations based on P. To further improve efficiency of use of N and P, farmers have the nutrient balance sheet available as an integrated management tool. Urea content in bulk milk has been introduced as a new indicator for the utilization of N in the diet. Also, fertilizer applications are improved. Furthermore, an experimental farm was set up to integrate all available expertise and analyze the resulting nutrient flows and farm performance.

Animal Feed↗
PubMed1996

First results from experiments performed with the ESA Anthrorack during the D-2 Spacelab mission.

In 1993 four astronauts performed physiological experiments on the payload "Anthrorack" during the second German Spacelab mission D-2. The Anthrorack set-up is a Spacelab double rack developed under the management of the European Space Agency. It consists of an ECHO machine, a respiratory monitoring system (gas analyzer with flow meter), a blood centrifuge, an ergometer, a finger blood pressure device, ECG, body impedance measurement device and a respiratory inductance plethysmograph. Experiment-specific equipment was used as well. Nineteen investigators performed experiments in the cardiovascular, pulmonary, fluid-renal and nutritional physiology area. Results on central venous pressure, ocular pressure, vascular resistance, cardiac output, tissue thickness and orthostatic intolerance are presented in the cardiovascular area. In the pulmonary area first results are mentioned on O2 transport perfusion and ventilation distribution and breathing pattern. From the fluid-renal experiments, data from diuresis, sodium excretion and hormonal determinations are given. Finally results from glucose metabolism and nitrogen turnover experiments are presented.

Adaptation, Physiological↗
PubMed1996

Swimming behavior of fish during short periods of weightlessness.

BACKGROUND: Birds and fish show tumbling and spinning movements when subjected to short periods of weightlessness during parabolic flight. The reason for this behavior is not clear. HYPOTHESIS: The semicircular canal system is a rotation-detecting device; however, it seems that linear accelerations have an influence, too. Microgravity induces rotatory sensations which leads to a compensatory behavior (e.g., rotatory movements). METHODS: The swimming behavior of goldfish was studied with the fish in four different conditions: normal fish (group I); fish with one eye recently removed (group II); fish with both eyes recently removed (group III); and fish with both eyes removed 10 months previously (group IV). Further, a group of naturally blind (e.g., not surgically treated) cavefish (group V) were involved in the study also. All procedures conformed to the guiding principles as required in the Dutch Law on Care and Use of Animals. RESULTS: Three main different patterns of abnormal swimming behavior could be observed: tumbling (pitch), corkscrew movements (pitch and roll), and spinning movements (roll). NF did not shown any special swimming pattern. One-eyed fish (group II): mostly corkscrew movements (62%). Blind fish (group III): a mixture of the three movements (17, 22 and 25%). Blind fish (group IV): mostly spinning movements (20%). Cavefish (group V): tumbling (21%), corkscrew movements (12%) and spinning movements (58%). CONCLUSION: Vision is the dominant cue, explaining the behavior of normal goldfish. When vision is absent, the fish relies on vestibular information with respect to orientation. The swimming behavior is presumably caused by an attempt to compensate rotatory illusions. As all movements were shown in the planes of the vertical canals, we conclude that these canals play a dominant role when fish are deprived from proper otolith information.

Animals↗
PubMed1994

A mutation in the insulin receptor that impairs proreceptor processing but not insulin binding.

Here we report the identification of a new mutation in the alpha-chain of the insulin receptor, changing Trp412 into Ser using DNA from consanguineous parents who gave birth to a child with leprechaunism. The mutant receptor was expressed stably in CHO and transiently in COS-1 cells. It was found that the Ser412 mutant is not cleaved into alpha- and beta-subunits and remains as a 210-kDa proreceptor at an intracellular site. This property of the mutant receptor is in line with the observed decreased insulin binding to the parental fibroblasts. Cross-linking experiments show that the Ser412 proreceptor is able to bind insulin with an affinity comparable to that of the wild-type alpha-chain. Despite its capacity to bind insulin, the mutant receptor is not autophosphorylated. We postulate that the patient was homozygous for the Trp412-->Ser mutation and that the mutation was responsible for the leprechaun phenotype. This is the first description of a transport-defective receptor with the mutation outside the tetrabasic processing site and a functional insulin binding domain. The ability of the Ser412 mutant to bind insulin in cross-linking experiments suggests that the impaired transport of the proreceptor to the cell surface is the primary cause for the binding defect to intact cells.

Animals↗
PubMed1993

Otolith responses in man during parabolic flight.

The influence of the varying gravito-inertial (Gz) force during parabolic flight on human otolith function was investigated experimentally. It was hypothesised that a varying Gz force profile initiates an otolith-ocular response that manifests itself in modulation of optokinetic nystagmus slow-phase eye velocity (OKN-SPV). Six subjects were seated in the ESA-Caravelle, facing perpendicular to the aircraft's longitudinal axis. The Gz profile was subsequently 1.8 Gz pull-up, 0 Gz microgravity, and 1.8 Gz recovery, each phase lasting about 20 s. Vertical eye movements were recorded with electro-nystagmography throughout the parabolic manoeuvre. Conditions were: (1) visual fixation, (2) darkness and (3) optokinetic stimulation of 50 deg/s in an upward or downward direction, projected on a cylindrical screen at 0.6 m viewing distance. No consistent nystagmus or gaze shift was measured in darkness. With optokinetic stimulation, however, ANOVA revealed downward enhancement of OKNSPV by 5 degrees/s in 1.8 Gz hypergravity, as compared with the 0 Gz condition and the 1 Gz condition. It is concluded that an otolith-ocular pathway modulates optokinetic eye movements in parabolic flight.

Adult↗
PubMed1993

Patients with lipodystrophic diabetes mellitus of the Seip-Berardinelli type, express normal insulin receptors.

Lipodystrophic diabetes mellitus of the Seip-Berardinelli type is a syndrome associated with insulin resistance and recessive inheritance. We have examined whether mutations in the insulin receptor are pathogenetic factors in this syndrome. Fibroblasts from three different patients with Seip-Berardinelli's lipodystrophy were tested for insulin binding, and insulin-stimulated receptor autophosphorylation. In addition, the coding region of both alleles of the iinsulin receptor gene was sequenced. No abnormalities in the number of high affinity insulin binding sites, and insulin-stimulated receptor autophosphorylation were detected. The insulin receptor related insulin-like growth factor I receptor also showed no functional changes. DNA sequence analysis of the amplified exons of the insulin receptor gene showed a silent mutation in patient 1 at codon Ser339, changing AGT to AGC. In patient 2 a heterozygous Met for Val substitution at position 985 was detected, which is a rare polymorphism. In patient 3 no mutations, other than described polymorphisms, were observed. These findings demonstrate that the primary genetic lesion in Seip-Berardinelli's lipodystrophy is outside the insulin receptor gene and that an involvement of the insulin-like growth factor I receptor is also unlikely.

Adolescent↗