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Biomedical subjects

S M Block

Publications and source records attributed to S M Block.

At least 37 records · Page 2Linked to original sources
PubMed1996

Prenatal diagnosis and pediatric neurosurgery.

Advances in realtime ultrasound imaging and a greater availability of high-quality ultrasound equipment have resulted in an increased number of congenital abnormalities being diagnosed prenatally in the last 10-15 years. In addition, testing for maternal serum alpha-fetoprotein, beta-human chorionic gonadotropin, and serum unconjugated estriol has allowed for more sensitive screening for congenital abnormalities. In response to this, in 1989 the Prenatal Diagnosis and Treatment Center was established at our institution to coordinate the care of fetuses and newborns with congenital malformations and to provide alternatives for the parents should the fetus not be carried to term. From January 1990 through June 1993, our group diagnosed 50 singleton pregnancies with various types of central nervous system disorders by the methods outlined above. Thirty-seven fetuses were diagnosed with neural tube defects. Of these, 5 were anencephalic and 1 had an encephalocele. The remaining 31 fetuses had meningomyeloceles with associated hydrocephalus. Of these 31, 18 fetuses were terminated prior to the age of viability as a result of our counseling and 13 fetuses were brought to term. Of the remaining 13 fetuses, 8 had hydrocephalus and 5 had various other diagnoses. Three of the eight hydrocephalic fetuses were either terminated, stillborn, or died following birth. Of the other 5 fetuses with hydrocephalus, 3 had shunts placed, 1 was followed with normal head growth, and 1 had normal ventricular size at birth. Using the methods available, the accuracy of diagnosis is very high, with only 1 fetus in this series being incorrectly diagnosed. Additionally the advantages of being able to counsel the parents regarding their unborn child allows them to make informed decisions. Accurate prenatal diagnosis plays a major role in the care of the fetus and in counseling parents prenatally for pediatric neurosurgical problems.

Abnormalities, Multiple↗
PubMed1996

Butylsoyamide increases unsaturation of fatty acids in plasma and milk of lactating dairy cows.

This study was designed to determine whether dietary butylsoyamide increased unsaturation of fatty acids in milk of lactating dairy cows. Nine Holstein cows were fed three diets in a 3 x 3 Latin square design, replicated three times. One diet was a control with no added fat, and the other two diets were supplemented (3.5% of the DM) with either soybean oil or butylsoyamide. Milk yields and DMI were similar for the three diets. Milk fat percentage and FCM were reduced by soybean oil, but not by butylsoyamide. Milk protein yield was reduced when butylsoyamide was fed, and milk fat yield was reduced when soybean oil was fed. The soybean oil supplement disrupted ruminal fermentation, causing total VFA and acetate concentrations to decline; the butylsoyamide supplement had no effect on ruminal VFA. The proportion of linoleic acid in plasma fatty acids was similar with the control (54.3%) and soybean oil (52.0%) diets but was higher with butylsoyamide (59.0%). Linoleic acid concentration in milk fat averaged 3.60, 4.77, and 6.28% for the control, soybean oil, and butylsoyamide diets, respectively. Conversion of soybean oil to butylsoyamide protected unsaturated fatty acids from ruminal biohydrogenation, causing linoleic acid to increase in the plasma and milk of dairy cows.

Acetates↗
PubMed1995

Transcription against an applied force.

The force produced by a single molecule of Escherichia coli RNA polymerase during transcription was measured optically. Polymerase immobilized on a surface was used to transcribe a DNA template attached to a polystyrene bead 0.5 micrometer in diameter. The bead position was measured by interferometry while a force opposing translocation of the polymerase along the DNA was applied with an optical trap. At saturating nucleoside triphosphate concentrations, polymerase molecules stalled reversibly at a mean applied force estimated to be 14 piconewtons. This force is substantially larger than those measured for the cytoskeletal motors kinesin and myosin and exceeds mechanical loads that are estimated to oppose transcriptional elongation in vivo. The data are consistent with efficient conversion of the free energy liberated by RNA synthesis into mechanical work.

Biophysical Phenomena↗
PubMed1995

Analysis of high resolution recordings of motor movement.

The development of in vitro motility assays for motor proteins has been accompanied by a parallel development of advanced optical instrumentation capable of recording motion at the molecular level. Devices now exist that can record displacements to better than 0.1 nm at bandwidths in excess of 10 kHz, and that can place controlled forces up to many pN on single motors. Ultra-high resolution data from experiments are now pouring in. The analysis and subsequent interpretation of experimental records, which are inevitably contaminated with high levels of thermal noise, remain an ongoing challenge. This essay examines selected issues relating to this challenge and discusses some alternative approaches.

Actins↗
PubMed1995

The cytologic evaluation of lipid-laden alveolar macrophages as an indicator of aspiration pneumonia in young children.

Gastroesophageal reflux with aspiration of feedings in infants and young children may be involved in the development of chronic lung damage. Our laboratory has utilized tracheal aspirates stained with oil red O to identify and quantitate lipid-laden alveolar macrophages as a marker of such aspiration. During the last 10 years, we have evaluated 244 tracheal aspiration smears in children. Although a few patients were up to 3 years old, the vast majority were infants. The cytologist looked for the presence of and the number of oil red O-positive macrophages on tracheal aspirate smears. The specimens were easily assigned grades of absent (grade = 0), low positive (grade 1: 1-25 lipid-laden macrophages), moderate positive (grade 2: 26-50 lipid-laden macrophages), and high positive (grade 3: > 50 lipid-laden macrophages). The grade was then correlated with the positive or negative clinical diagnosis of gastroesophageal reflux with aspiration. We believe the cytologic evaluation and grading of oil red O-stained tracheal aspirates for lipid-laden macrophages is valuable in identifying these patients with gastroesophageal reflux and aspiration.

Azo Compounds↗
PubMed1994

Fluctuation analysis of motor protein movement and single enzyme kinetics.

We studied fluctuations in the displacement of silica beads driven by single molecules of the motor protein kinesin, moving under low mechanical loads at saturating ATP concentrations. The variance in position was significantly smaller than expected for the case of stepwise movement along a regular lattice of positions with exponentially distributed intervals. The small variance suggests that two or more sequential processes with comparable reaction rates dominate the biochemical cycle. The low value is inconsistent with certain recently proposed thermal ratchet models for motor movement as well as with scenarios where the hydrolysis of a single ATP molecule leads to a cluster of several steps. Fluctuation analysis is a potential powerful tool for studying kinetic behavior whenever the output of a single enzyme can be monitored.

Animals↗
PubMed1994

Force and velocity measured for single kinesin molecules.

We measured the force-velocity curves of single kinesin molecules attached to silica beads moving in an in vitro motility assay. Optical trapping interferometry was used to track movement with subnanometer precision and to apply calibrated, pN-sized forces to the beads. Velocity decreased linearly with increasing force, and kinesin molecules moved against applied loads of up to 5-6 pN. Comparison of force-velocity curves at limiting and saturating ATP concentrations suggests that the load-dependent diminution in kinesin velocity may be due to a decrease in the net displacement per molecule of ATP hydrolyzed, not simply to a slowing of the ATP turnover rate; kinesin would therefore appear to be a loosely coupled motor.

Adenosine Triphosphate↗
PubMed1994

A mutant hook-associated protein (HAP3) facilitates torsionally induced transformations of the flagellar filament of Escherichia coli.

Two mutants with defects in hook-associated protein 3 (HAP3) were isolated that exhibit impaired swimming only when they interact with a solid surface or a semisolid matrix. Motility and chemotaxis were normal in liquid media, even in media containing viscous agents, but cells failed to swarm in 0.28% agar. Mutants appeared to carry a full complement of flagella of normal configuration and length. However, filaments rotating counterclockwise close to a glass surface transformed from normal to straight, while filaments rotating clockwise transformed from curly to straight. Both transformations propagated from base to tip, as expected if torsionally induced. The mutations mapped to the middle of flgL, to structural gene for HAP3, and sequence analysis revealed the same coding change in both mutants: a substitution of cysteine for arginine 168. Our results show that the ability of a filament composed of normal flagellin subunits to resist mechanical stress depends on the structure of the protein (HAP3) to which it is attached at its base. The N-terminal sequence of HAP3 was found to be similar to the N-terminal sequence of flagellin, and the possibility that it provides a nucleation site for the C-terminal region of flagellin is discussed.

Amino Acid Sequence↗
PubMed1994

Alkaline phosphatase histochemical staining in the study of germinal matrix hemorrhage and brain vascular morphology in a very-low-birth-weight neonate.

We evaluated the utility of alkaline phosphatase (AP) histochemical staining for studying intraparenchymal vascular morphology in the brain of a 31-wk-gestation (1480 g) neonate who died of respiratory insufficiency after 23 h. In this baby, afferent cerebral vessels (arteries, arterioles, and capillaries) stained with AP, whereas efferent vessels (venules, veins) did not. The large periventricular channels in the germinal matrix were determined to be veins, according to AP staining criteria. Arterioles connected with these large periventricular veins after passing through 4- to 6-microns capillaries. Branchings and connections of the cerebral circulation were conventional; i.e. no arterial rete or arteriovenous shunts were found. With this method of differential vascular staining, bleeding in the germinal matrix was found to be perivenous only. No dilated capillaries or arterioles were seen. Smooth muscle was identified in extrastriatal medullary arteries. This preliminary investigation suggests that AP histochemical staining is an excellent method for studying brain vascular morphology and pathology of the very-low-birthweight neonate.

Adult↗
PubMed1993

Direct observation of kinesin stepping by optical trapping interferometry.

Do biological motors move with regular steps? To address this question, we constructed instrumentation with the spatial and temporal sensitivity to resolve movement on a molecular scale. We deposited silica beads carrying single molecules of the motor protein kinesin on microtubules using optical tweezers and analysed their motion under controlled loads by interferometry. We find that kinesin moves with 8-nm steps.

Adenosine Triphosphate↗
PubMed1993

Response to Haemophilus influenzae type b conjugate vaccine in chronically ill premature infants.

Twenty-two premature infants with chronic lung disease (median gestational age 28 weeks) received polyribosylribitol phosphate-outer membrane protein conjugate Haemophilus vaccine at 2 and 4 months of chronologic age. The proportions with antibodies to polyribosylribitol phosphate at levels > 1 microgram/ml after doses 1 and 2 were 27% and 55%; geometric mean titers were 0.43 and 0.73 microgram/ml, significantly lower than values for term infants.

Age Factors↗
PubMed1992

Making light work with optical tweezers.

Microscopic objects, including biological material, can be remotely manipulated with tightly focused beams of infrared laser light. The use of optical traps, or 'optical tweezers', holds great promise for noninvasive micromanipulation and mechanical measurement in cell biology. Optical tweezers are the 'tractor beams' of today's technology.

Animals↗