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S Smit

Publications and source records attributed to S Smit.

8 recordsLinked to original sources
PubMed1991

Control of cAMP-induced gene expression by divergent signal transduction pathways.

A compilation of literature data and recent experiments led to the following conclusions regarding cyclic adenosine 3':5' monophosphate (cAMP) regulation of gene expression. Several classes of cAMP-induced gene expression can be discriminated by sensitivity to stimulation kinetics. The aggregation-related genes respond only to nanomolar cAMP pulses. The prestalk-related genes respond both to nanomolar pulses and persistent micromolar stimulation. The prespore specific genes respond only to persistent micromolar stimulation. The induction of the aggregation- and prestalk-related genes by nanomolar cAMP pulses may share a common transduction pathway, which does not involve cAMP, while involvement of the inositol 1,4,5-trisphosphate (IP3)/Ca2+ pathway is unlikely. Induction of the expression of prespore and prestalk-related genes by micromolar cAMP stimuli utilizes divergent signal processing mechanisms. cAMP-induced prespore gene expression does not involve cAMP and probably also not cyclic guanosine 3'.5' monophosphate (cGMP) as intracellular intermediate. Involvement of cAMP-induced phospholipase C (PLC) activation in this pathway is suggested by the observation that IP3 and 1,2-diacylglycerol (DAG) can induce prespore gene expression, albeit in a somewhat indirect manner and by the observation that Li+ and Ca2+ antagonists inhibit prespore gene expression. Cyclic AMP induction of prestalk-related gene expression is inhibited by IP3 and DAG and promoted by Li+, and is relatively insensitive to Ca2+ antagonists, which indicates that PLC activation does not mediate prestalk-related gene expression. Neither prespore nor prestalk-related gene expression utilizes the sustained cAMP-induced pHi increase as intracellular intermediate.

Cyclic AMP↗
PubMed1984

Iron uptake by Chinese hamster fibroblasts from human transferrin.

The manner of uptake or iron by Chinese hamster fibroblasts, type DON, from human transferrin was investigated by means of replacement studies, in which the cells that were incubated with 125I-labelled human transferrin were chased with non-radioactive transferrin for only a few minutes. The results did not support the reversible endocytosis hypothesis for the uptake of iron from transferrin. The uptake of iron measured as 59Fe during several cell divisions was found to be a function of time and cell number. It was found that the total uptake of iron in the harvests was directly proportional to the incubation, and that the uptake per 10(6) cells levelled off in the course of time.

Animals↗
PubMed1981

Polynuclear iron compounds in human transferrin preparations.

During commonly used saturation procedures of transferrin with iron compounds, both as ferri and ferrous, polynuclear iron compounds are easily formed, even when nitrilotriacetate (NTA) is used as a strong iron ligand. The presence of these nonspecific bound irons is demonstrated with Mossbauer spectroscopy and with electronic optical spectroscopy. But no evidence, however, has been found of two different iron binding sites. Because dialysis is not able to remove all polynuclear iron, an easy method with gel filtration has been developed that does remove the polynuclear iron. Some notes are made about the often used method, in transferrin biochemistry, of saturation determination, i.e. the quotient of the absorbances of 470 and 280 nm.

Binding Sites↗
PubMed1980

Analysis of the urine of the okapi (Okapia johnstoni).

The urine of six adult and two juvenile okapis housed in The Royal Rotterdam Zoological and Botanical Gardens were analysed qualitatively for the presence of protein, glucose, bilirubin, nitrite, blood and ketones and the pH was measured. Quantitative analyses were undertaken for osmolality, urea, creatinine and glucose. The results of the analyses were generally unremarkable with the exceptions of pH, glucose and in some cases the urea/creatinine ratios. However, with the exception of the glucose these other results are physiologically normal. One possible explanation for the presence of glucose in the urine of the okapis is dietary. In the wild these animals are folivorous and thus they may not be able to cope with the high level of sugar presented to them in their captive diet. However, it must be emphasised that this condition has no apparent ill effects on the animals which are in good health and are breeding successfully.

Animals↗
PubMed1977

Porphyrin synthesis in blood cells of patients with erythropoietic protoporphyria.

The protoporphyrin accumulation observed in the red blood cells of patients with erythropoietic protoporphyria can be explained by decreased activity of the enzyme heme synthetase or by increased production of porphyrins in the affected cells. In literature experimental evidence both for a partial heme synthetase deficiency and for increased porphyrin biosynthesis has been presented. In a group of ten patients with erythropoietic protoporphyria the biosynthesis of porphyrins from delta-aminolevulinic acid and from glycine-succinic acid appeared to be normal in peripheral blood cells. These results are consistent with the partial heme synthetase deficiency previously found to be the basic defect of this disease.

Aminolevulinic Acid↗
PubMedDate not supplied

Evaluating the evaluators: interrater reliability on EMT licensing examinations.

INTRODUCTION: Current methods of evaluating the technical competence of Michigan emergency medical technician (EMT) licensure candidates are subjective and potentially unreliable. Evaluators are required to attend a workshop before evaluating practical examination candidates. Despite the workshop, there is too much score variation and not enough observational consistency on the standardized examination. OBJECTIVE: To determine the level of rater reliability for evaluators of EMT practical examinations. METHODS: Data were collected from 104 licensed instructor-coordinators (ICs). Participants watched and scored two practical examinations simulated on videotape, one passing and one failing performance. Variation in student score and level of evaluator agreement concerning skill performance were determined. Michigan's basic EMT practical examination scoring instrument was used. RESULTS: Nine basic EMT, 9 EMT specialist, and 86 EMT-paramedic ICs participated. Thirty-four percent had high school diplomas, 43% associate's degrees, 19% bachelor's degrees, 3% master's degrees, and 1% a doctoral degree. The ICs averaged 14 years of provider experience, and 6.35 years as an IC. The average score for scenario 1 (passing) was 86.4% (SD = 9.15, range = 53). An 80% score is required to pass. Nine ICs (9%) failed the student. Scenario 1 evaluator agreement was 79.4%. The average score for scenario 2 (failing) was 60.9% (SD = 11.57, range = 57). Seventeen ICs (18%) gave the student a passing score. Scenario 2 evaluator agreement was 67.8%. There was no significant difference in student scores based on evaluator level of education, licensure, or evaluator workshop attendance for either scenario. CONCLUSION: Notable variation in scores given by evaluators for a single observed student, combined with low levels of evaluator agreement about skill performance, suggests that evaluators do not reliably rate student performance using the Michigan practical examination instrument.

Educational Measurement↗