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Biomedical subjects

F C Stevens

Publications and source records attributed to F C Stevens.

At least 19 recordsLinked to original sources
PubMed1994

The development of a short generic version of the Sickness Impact Profile.

This study concerns the development of a short version of a well-known and much used clinimetric instrument called the Sickness Impact Profile (SIP). The SIP is a generic measure of functional status. Based on findings of a principal components analysis of over 800 SIPs from a multi-diagnostic population, a selection of 68 items divided over 6 dimensions was made and initially tested. As no support was found for the statistical validity of the categorical structure of the original SIP, a new structure, discovered through principal components analysis, was used as the basis for selecting items. Comparison of the scores on the selection with information provided by the original SIP showed very promising results: the 68 item selection may serve as a valid short SIP-version.

Female↗
PubMed1994

Community nursing in Belgium, Germany and The Netherlands.

This paper contains a comparative study on community nursing in the Netherlands, Belgium and Germany, carried out in the region around Maastricht, where the borders of the three countries meet. The well-known problem of comparative studies (the incomparability of concepts and data) has been solved by using the same measuring instruments in the three countries. The comparison between the countries was on three aspects: the level of care dependency of the patients, the type and number of services provided and the nurses' job interpretation and job satisfaction. During 1 week in June or September 1991, 89 community nurses made records of all their home visits and nursing activities. In total the community nurses paid 5165 home visits to provide care to 1796 patients. The results indicate that both the level of care dependency of the patients as well as the type of care provided differs between the three countries. Belgian community nurses have the highest number of patients with a high level of care dependency. Curative services like technical nursing care and domestic care are most frequently provided by the German and Belgian community nurses. Informing, educating and supporting care is most frequently provided by the Dutch community nurses. The German community nurses spend less time on administration activities. With respect to job interpretation and job satisfaction the following results were found. The Dutch community nurses mentioned in their job interpretation many more preventive tasks, whereas the German community nurses more often mentioned domestic tasks. Concerning the hygienic and technical tasks, no significant differences were found between the three countries. Finally, job satisfaction is lowest in the Netherlands. Dutch community nurses are less satisfied with the work organization and the possibilities of autonomy and professionalization than the German and Belgian community nurses.

Belgium↗
PubMed1989

[Job satisfaction of physicians in academic and general hospitals].

Based on a study of 20 medical departments (general surgery, internal medicine, radiology) an analysis is presented of variables which may account for differences in work satisfaction. The results show: (a) (experienced) work load correlates negatively with work satisfaction; (b) satisfied physicians define their medical domain more broadly than dissatisfied physicians. Besides, they do not regard their salary as an important aspect of their work. In general, radiologists are most satisfied with their work, internists least; medical specialists are more satisfied than residents. In the discussion it is argued that hospital physicians prefer regularity in their work, combined with a professional work climate. In terms of the growing bureaucratization of the physician's work it is concluded that satisfaction is positively influenced by standardization of work processes and negatively by external pressures which limit professional autonomy.

Academic Medical Centers↗
PubMed1983

Calmodulin: an introduction.

Calmodulin is the most widely distributed and most versatile member of a family of calcium-binding proteins which probably serve as receptors for the Ca2+ signal. Through the regulation of a wide variety of intracellular enzymes, calmodulin plays a key role in many physiological processes. An understanding of the different mechanisms by which calmodulin exerts its influence is beginning to emerge and an interesting hypothesis regarding the interrelationship between the cAMP and Ca2+ second messenger systems has recently been put forward.

Amino Acid Sequence↗
PubMed1979

Circular dichroism studies of native and chemically modified Ca2+-dependent protein modulator.

The structural features of the native Ca2+-dependent protein modulator and two chemically modified derivatives, namely, nitrotyrosyl modulator and alkylated modulator, were examined by circular dichroism. The binding of Ca2+ to the native molecule was accompanied by an increase in helical content from 40 to 49%, with little effect on the local environments of aromatic residues in the modulator. The Mg2+ and Mn2+ do not elicit the conformational change induced by the binding of Ca2+, which also stabilizes the modulator against urea denaturation. The overall secondary structure of nitrotyrosyl modulator is indistinguishable from that of the native protein and undergoes a similar conformational change upon binding Ca2+. These observations are in agreement with the fact that nitration has no effect on modulator functions. Furthermore, nitrotyrosyl modulator interacts with troponin I only in the presence of Ca2+, as detected by circular dichroism (cd). On the other hand, alkylation of five methionine residues on the modulator with benzyl bromide affects protein conformation, as evidenced by a reduced helical content of only 35%. Alkylated modulator retains the ability of the native protein to bind Ca2+ although the affinity of this derivative for Ca2+ is reduced some three orders of magnitude relative to the native protein, with Kd = 3.2 X 10(-4) M. The results with the alkylated modulator, in conjunction with previous cd studies on N-chlorosuccinimide oxidized modulator are utilized to advance a model for the Ca2+ activation of modulator protein, based on three conformational states of the molecule.

Alkylation↗
PubMed1978

Chemical modification studies on the Ca2+-dependent protein modulator: the role of methionine residues in the activation of cyclic nucleotide phosphodiesterase.

Methionine residues have been implicated in the activation of cyclic nucleotide phosphodiesterase by the Ca2+-dependent protein modulator [Walsh, M., & Stevens, F.C. (1977) Biochemistry 16,2742-2749]. Treatment of the modulator with N-chlorosuccinimide in the presence of Ca2+ resulted in selective oxidation of methionine residues at positions 71,72, 76, and, possibly, 109 in the modulator sequence. These residues lie on the surface of the molecule exposed to solvent. This modification has several effects on the modulator protein: (1) the Ca2+-binding properties of the oxidized modulator are changed with apparent loss of high-affinity binding sites, (2) the oxidized protein no longer interacts with phosphodiesterase, and (3) troponin C like activities, viz., Ca2+-dependent change in mobility on urea-polyacrylamide gel electrophoresis and formation of a urea-stable complex with troponin I, are lost upon oxidation of the modulator. The phosphodiesterase binding domain of the modulator protein appears to be located between the second and third Ca2+-binding loops, a region of the molecule known from previous partial proteolysis studies [Walsh, M., Stevens, F.C., Kuznicki, J., & Drabikowski, W.(1977), J. Biol. Chem. 252, 7440-7443] to be exposed in the presence of Ca2+.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1978

Circular dichroism studies on Ca2+-dependent protein modulator oxidized with N-chlorosuccinimide.

The structural features and Ca2+-binding properties of native and N-chlorosuccinimide-oxidized modulator protein were compared by circular dichroism. In the presence of Ca2+,the far-UV spectra of native and oxidized modulator protein are virtually indistinguishable, indicating that oxidation of surface methionine residues does not alter the overall conformation of the molecule. In the absence of Ca2+, however, the circular dichroism spectra of native and oxidized modulator are different with calculated helical contents of 40% and 26%, respectively. As judged by circular dichroism titration studies, the native modulator contains both high-(Kd = 1.9 X 10(-7) M) and low-affinity (Kd = 4 X 10(-4) M) Ca2+-binding sites, whereas the modified modulator appears to possess only low-affinity sites (Kd = 3.8 X 10(-4) M). The reduced secondary structure in Ca2+-free oxidized modulator protein may account for the absence of high affinity Ca2+ binding sites.

Animals↗
PubMed1978

Purification and characterization of a Ca2+-binding protein in Lumbricus terrestris.

A Ca2+-binding protein which is capable of activating mammalian Ca2+-activatable cyclic nucleotide phosphodiesterase has been purified from Lumbricus terrestris and characterized. This protein and the Ca2+-dependent protein modulator from bovine tissues have many similar properties. Both proteins have molecular weights of approximately 18,000, isoelectric points of about pH 4, similar and characteristic ultraviolet spectra, and similar amino acid compositions. Both proteins bind calcium ions with high affinity. However, the protein from Lumbricus terrestris binds 2 mol of calcium ions with equal affinity, Kdiss = 6 X 10(-6) M, whereas the Ca2+-dependent protein modulator from bovine tissues binds 4 mol of calcium ions with differing affinities. Although the Ca2+-binding protein of Lumbricus terrestris activates the Ca2+-activatable cyclic nucleotide phosphodiesterase from mammalian tissues, we have failed to detect the existence of a Ca2+-activatable phosphodiesterase activity in Lumbricus terrestris. The activation of phosphodiesterase by the Ca2+-binding protein from Lumbricus terrestris is inhibited by the recently discovered bovine brain modulator binding protein (Wang, J. H., and Desai, R. (1977) J. Biol. Chem. 252, 4175-4184). Since the modulator binding protein has been shown to associate with the mammalian protein modulator to result in phosphodiesterase inhibition, it can be concluded that the Lumbricus terrestris Ca2+-binding protein also associates with the bovine brain modulator binding protein. Attempts to demonstrate the existence of a similar modulator binding protein in Lumbricus terrestris have been unsuccessful.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1977

Purification of a Ca2+-activatable cyclic nucleotide phosphodiesterase from bovine heart by specific interaction with its Ca2+-dependent modulator protein.

A Ca2+-activatable cyclic nucleotide phosphodiesterase from bovine heart can be eluted from a DEAE-cellulose column either in the free form by buffers containing 0.1 mM ethylene glycol bis(beta-aminoethyl ether)N-N,N'N'-tetraacetic acid (EGTA) or as a complex of the enzyme with its protein modulator by buffers containing 0.01 mM CaCl2. A purification procedure based primarily on the significantly different affinity of the two forms of the enzyme for DEAE-cellulose was developed for the purification of the enzyme from bovine heart. The procedure involves ammonium sulfate fractionation, three chromatographic steps on DEAE-cellulose, and gel filtration on Sephadex G-200 with a 5000-fold purification over the crude extract. The purified enzyme has a specific activity of 120 mumol of cAMP/mg/min, can be activated 5-fold by Ca2+, but is only 80% pure as judged by analytical disc gel electrophoresis. The purified enzyme is unstable but can be stabilized by addition of Ca2+ and the protein modulator; this is in contrast to the less pure preparations of Ca2+-activatable phosphodiesterase which are destabilized by the protein modulator in the presence of Ca2+.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1976

Comparison of calcium-binding proteins. Bovine heart and brain protein activators of cyclic nucleotide phosphodiesterase and rabbit skeletal muscle troponin C.

In previous studies we have shown that the activation of bovine heart cyclic nucleotide phosphodiesterase by purified protein activator is completely dependent on the presence of Ca2+ and that the protein activator Ca2+ complex is probably the true activator for the enzyme (Teo, T.S. and Wang, J.H. (1973) J. Biol. Chem. 248, 5930-5955). More recent studies have led us to believe that the mechanism of the Ca2+ activation of phosphodiesterase resembles that of the Ca2+ activation of muscle contraction and that the protein activator may play a role similar to troponin. In the present study we show that the protein activator resembles rabbit muscle troponin C in amino acid composition, molecular weight, isoelectric point, and ultraviolet absorption spectrum. Preliminary structural studies also indicate that these two proteins may have evolved from a common ancestral protein through gene duplication. This argument is strengthened by the finding that the tryptic peptide map of the bovine heart protein activator is indistinguishable from that of the bovine brain phosphodiesterase activator protein for which preliminary sequence information also suggests homology to troponin C (Watterson, D.M., Harrelson, W.G., Jr., Keller, P.M., Sharief, F., and Vanaman, T.C. (1976) J. Biol. Chem. 251, 4501-4513).

Amino Acid Sequence↗