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Biomedical subjects

L Rappaport

Publications and source records attributed to L Rappaport.

At least 109 records · Page 6Linked to original sources
PubMed1983

Children's descriptions of their developmental dysfunctions. Field testing of a self-administered student profile.

To assess schoolchildren's own perceptions of their neurodevelopmental, social, and academic status, a self-administered student assessment has been developed. Using this instrument in conjunction with teacher ratings, 420 fourth- and sixth-grade students in a suburban community were compared with 110 grade-matched patients in a hospital referral clinic for school problems. In the community group, sixth graders reported fewer concerns than fourth graders in all developmental areas. Boys reported more difficulties in attention and memory, and girls reported more difficulties in gross motor skills. Teachers rated boys as having more problems than girls in all academic and behavioral areas, except mathematics. There was a significant correlation between teacher evaluations and total scores on the profile. Differences were found between the community and clinical groups on the total assessment and in most individual areas of development. The Self-Administered Student Profile can enhance evaluations of learning disorders, while eliciting issues for counseling such children.

Boston↗
PubMed1983

Phosphorylation of a 43 kdaltons protein from rat heart by a calmodulin-dependent protein kinase.

The Ca2+ -dependent phosphorylation of proteins has been recognized as a major regulatory mechanism of biological processes. In the heart, protein kinases that are activated by Ca2+ include phosphorylase kinase, myosin light chain kinase, phospholamban kinase [review in 4], and the kinases responsible for phosphorylation of endogenous proteins in the membrane [11] and soluble [6] fractions of the cell. All of these Ca2+-dependent enzymes require the presence, either as an enzyme subunit or as a cofactor, of calmodulin, a Ca2+-binding protein which is involved in various other Ca2+-requiring reactions or processes [review in 3]. We demonstrate here the presence, in the rat heart, of a soluble calmodulin-dependent protein kinase which seems different from those already described in this tissue. The substrate for this enzyme is a 43 kdaltons protein, present in the same soluble fraction.

Animals↗
PubMed1983

Effect of photosynthetic inhibitors and uncouplers of oxidative phosphorylation on nitrate and nitrite reduction in barley leaves.

The effects of several photosynthetic inhibitors and uncouplers of oxidative phosphorylation on NO(3) (-) and NO(2) (-) assimilation were studied using detached barley (Hordeum vulgare L. cv Numar) leaves in which only endogenous NO(3) (-) or NO(2) (-) were available for reduction. Uncouplers of oxidative phosphorylation greatly increased NO(3) (-) reduction in both light and darkness, while photosynthetic inhibitors did not.The NO(2) (-) concentration in the control leaves was very low in both light and darkness; 98% or more of the NO(2) (-) formed from NO(3) (-) was further assimilated in control leaves. More NO(2) (-) accumulated in the leaves in light and darkness in the presence of photosynthetic inhibitors. Of this NO(2) (-), 94% or more was further assimilated. It appears that metabolites, either external or internal to the chloroplast, capable of reducing NADP (which, in turn, could reduce ferredoxin via NADP reductase) might support NO(2) (-) reduction in darkness and light when photosynthetic electron flow is inhibited by photosynthetic inhibitors.NITRITE ASSIMILATION WAS MUCH MORE SENSITIVE TO UNCOUPLERS IN DARKNESS THAN IN LIGHT: in darkness, 74% or more of NO(2) (-) formed from NO(3) (-) was further assimilated, whereas in light, 95% or more of the NO(2) (-) was further assimilated.

Journal Article↗
PubMed1983

Distribution of myosin isozymes within single cardiac cells. An immunohistochemical study.

Isozymes of myosin have been localized with respect to individual cardiac myocytes in hearts from 3-week-old, adult controls, and adult hypophysectomized rats, and in cultured cardiac cells. For this purpose, affinity-purified antibodies reacting specifically with the heavy chains of each of the two major myosin isozymes of adult rat heart, V1 and V3, were used. The distribution of the two isomyosins was determined by double immuno-labeling of the same cell, V1 myosins being revealed by rhodamine and V3 myosins by fluorescein. A procedure is described which allows optimum immunological visualization of the myosin filaments of rod-shaped isolated myocytes. It was found that the response of the cardiac cells to the two antimyosins varied depending on the state of the animal. In 3-week-old rats, all cells were stained with the anti-V1, and almost none with the anti-V3 myosin. In the hypophysectomized animals, on the contrary, all cells were stained with the anti-V3 and none with the anti-V1. A mixed pattern of reactivity was observed in adult controls since 50% of the cells reacted with the anti-V1, 10% with the anti-V3, and 40% with both antibodies. In the latter case, the distributions of V1 and V3 reactivities were homogeneous throughout the cell, and absolutely superimposable. The same double reactivity and homogeneous repartition were observed in cultured cells. These findings indicate that myocytes from adult rat myocardium are heterogeneous in terms of their isomyosins content and show for the first time that two isomyosins can coexist and be equally distributed in one cardiac cell. These observations are relevant to the regulation of individual heart cell contractility.

Animals↗
PubMed1983

Immunological quantitation and localization of tubulin in adult rat heart isolated myocytes.

Isolated myocytes were purified from adult rat heart. Identification and localization of microtubules and quantitation of tubulin in these cells were performed by immunochemical procedures. Antibodies were raised against brain tubulin and purified by affinity chromatography. An enzyme-linked immunosorbent assay, ELISA, was developed for quantitation of tubulin. It allowed the measurement of 10 to 500 ng of tubulin. Tubulin content in adult rat cardiac myocytes was found to be approximately 10 micrograms per 100 mg of the total protein content. By means of a double immunofluorescence technique, the microtubule network, identified with antitubulin, was studied in reference to the sarcomeric A band labeled with antibodies specific to myosin heavy chains. The basis for identifying the microtubule network have included the use of specific antitubulin immunoglobulins and the sensitivity of the specific labeling of the network to antimitotic drugs and low temperature. It was found that microtubules were organized mainly around the nuclei, with important concentrations at the poles, showing extensions in the cone and in the cytoplasm as loosely organized loops. The shape of adult cardiac myocyte was not dependent upon the integrity of the microtubule network.

Alkaloids↗
PubMed1980

Uptake and subcellular compartmentation of gibberellin a(1) applied to leaves of barley and cowpea.

The uptake and subcellular accumulation of gibberellin A(1) (GA(1)) by leaves and protoplasts of barley (cv. Numar) and cowpea (cv. Blackeye pea No. 5) were investigated.Uptake of GA(1) by cowpea leaves is optimal at pH 5.8 and occurs by a saturable, probably carrier-mediated process having a half-maximal velocity at 10 to 20 micromolar. Uptake by both barley and cowpea leaves is inhibited by low temperature (+4 C) and the metabolic inhibitors 2,4-dinitrophenol and azide and is stimulated by ATP. Mesophyll protoplasts isolated from leaves fed radioactive GA(1) retain 20 to 80% of the radioactivity incorporated by excised leaves.The subcellular localization of the [(3)H]GA was determined by lysing protoplasts and separating subcellular organelles by density gradient centrifugation. Less than 5% of the incorporated [(3)H]GA was found associated with chloroplasts, mitochondria, nuclei, or other organelles or membranes with densities in sucrose gradients greater than 1.15 grams per cubic centimeter. Fifty to 100% of the [(3)H]GA was found in vacuoles. Isolated vacuoles were judged to be free of contamination by cytoplasm using phosphoenolpyruvate carboxylase as a marker enzyme. Osmotic breakage of vacuoles or protoplasts released > 95% of the [(3)H]GA, suggesting that GA is associated with the vacuolar sap rather than with the tonoplast membrane.

Journal Article↗
PubMed1979

Synthesis of a possible precursor of alpha-amylase in wheat aleurone cells.

alpha-Amylase from wheat aleurone (Triticum aestivum) was synthesized in a S-150 wheat germ readout system using polysomes, and a messenger RNA-dependent reticulocyte lysate system using polyadenylic acid [poly(A)]-enriched RNA. The product was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, precipitation by specific lambda-globulin for alpha-amylase, and proteolysis. Two immunoprecipitated products were synthesized from the readout system, the predominant species migrating coincidentally with authentic alpha-amylase on sodium dodecyl sulfate-polyacrylamide gels. A putative precursor, 1,500 daltons larger, was evident but was less abundant. The relationship between the two polypeptides was established by proteolytic analysis using Staphylococcus aureus V8 protease. At least nine fragments were generated and were identical in both species. The poly(A)-enriched RNA synthesized only the putative precursor in the reticulocyte lysate system. Attempts to process the precursor to the mature size of alpha-amylase failed. These findings are discussed in connection with the signal hypothesis (proposed for the transport of proteins across membranes) and the mode of secretion of alpha-amylase in aleurone cells.

Journal Article↗
PubMed1976

Phosphorylation of microtubule-associated proteins.

1. Tubulin is not an adenosine-3':5'-monophosphate-dependent (cyclic-AMP-dependent) protein kinase. Both entities have been clearly separated by sucrose gradient ultracentrifugation. With a tubulin preparation obtained by the polymerization-depolymerization technique protein kinase had a sedimentation coefficient of 8.7 S whereas tubulin sedimented with 6.4 S. After preincubation with both cyclic AMP and histone the kinase dissociated into its catalytic subunit with a sedimentation coefficient of 3.4 S. 2. Tubulin prepared by the polymerization-depolymerization technique was neither phosphorylated in vivo nor in vitro. On the contrary if this preparation was further purified by the Weisenberg's procedure (DEAE-Sephadex batch absorption) before incubation with [gamma-32 P]ATP, phosphorylation occurred. Thus, phosphorylation depended on the method used to purify tubulin i.e. was likely to an an artefact.

Brain↗
PubMed1975

Metabolism of Tritiated Gibberellins in d-5 Dwarf Maize: I. In Excised Tissues and Intact Dwarf and Normal Plants.

Metabolism of [(3)H]gibberellin A(1) ([(3)H]GA(1)) was followed in intact seedlings and excised apices and leaf tissue of both dwarf and normal (tall) plants of d-5 maize (Zea mays L.). The three metabolites produced were tentatively identified as [(3)H]GA(s), [(3)H]GA(s)-glucoside ([(3)H]GA(s)-glu), and [(3)H]GA(1)-X, an unknown.In 3-hour, pulse-labeling experiments with tissues of incubated, expanding leaves, more than 70% of the [(3)H]GA(1) taken up was metabolized to the three products within 12 to 15 hours. [(3)H]GA(1) fed to the roots of 7-day-old seedlings was readily translocated to the leaves, and all three metabolites were found in both roots and leaves. [(3)H]GA(1)-X was the major metabolite in roots, whereas in leaves the major metabolite was [(3)H]GA(s)-glu. There were no consistent differences in [(3)H]GA(1) metabolism between dwarf and normal plants, indicating that dwarfism in d-5 maize is not associated with modified GA(1) metabolism.In excised, mature leaf tissue, [(3)H]GA(1) metabolism was slower than in excised, young leaf tissue. Mature leaf tissues produced [(3)H]GA(s)-glu as by far the major metabolite, with [(3)H]GA(s) and [(3)H]GA(1)-X as minor metabolites. In contrast, in young leaves the three metabolites appeared sequentially in significant proportions: [(3)H]GA(8) first, followed by [(3)H]GA(s)-glu and, finally, [(3)H]GA(1)-X.

Journal Article↗
PubMed1975

Metabolism of Tritiated Gibberellins in d-5 Dward Maize: II. [H]Gibberellin A(1), [H]Gibberellin A(3), and Related Compounds.

After 30 minutes of incubation of young leaf sections of d-5 maize (Zea mays L.) in [(3)H]gibberellin A(1) ([(3)H]GA(1)), the metabolite [(3)H]GA(8) was present in significant amounts, with a second metabolite, [(3)H]GA(8)-glucose ([(3)H]GA(8)-glu), appearing soon after. A third [(3)H]GA(1) metabolite, the polar uncharacterized conjugate [(3)H]GA(1)-X, took more than 1 hour to appear. The protein synthesis inhibitor cycloheximide inhibited the production of all [(3)H]GA(1) metabolites, indicating a possible protein synthesis requirement for [(3)H]GA(1) metabolism.By preincubating leaf sections in unlabeled GA(1) before exposure to [(3)H]GA(1) or by reducing the specific radioactivity of the [(3)H]GA(1) supplied, it was possible to reduce greatly the conversion of radioactive GA(1) to [(3)H]GA(8)-glu, without affecting conversion to [(3)H]GA(1)-X. Increasing the molar concentration of the [(3)H]GA(1) fed greatly increased the molar yield of [(3)H]GA(1)-X, whereas the molar yields of [(3)H]GA(8) and [(3)H]GA(8)-glu were much less affected.The principal metabolite of [(3)H]GA(3) was a very polar compound having chromatographic properties similar to those of the conjugate [(3)H]GA(1)-X produced from [(3)H]GA(1). The naturally occurring GAs [(3)H]GA(1), [(3)H]GA(3), and [(3)H]tetrahydroGA(3) were metabolized to a much greater extent than were the artifical derivatives [(3)H]ketoGA(1), [(3)H]GA(1)-methyl ester, and [(3)H]pseudoGA(1). Only [(3)H]GA(1) and [(3)H]GA(3), with their identical D ring structures, were converted to [(3)H]GA(1)-X type compounds; [(3)H]-ketoGA(1) and [(3)H]tetrahydroGA(3), with modified D rings, were not converted to this type of conjugate.

Journal Article↗
PubMed1974

Selective binding of (3H)gibberellin A1 by protein fractions from dwarf pea epicotyls.

A homogenate from dwarf pea seedlings that had been treated with [(3)H]gibberellin A(1) was separated by Sephadex G-200 into two protein fractions, of high and intermediate molecular weight, with affinity for [(3)H]gibberellin A(1). Neither fraction bound [(3)H]gibberellin A(8), the only metabolite of [(3)H]gibberellin A(1) detected in significant quantity in extracts of pea seedlings. These proteinhormone complexes were noncovalently bound, as evidenced by their rapid disruption in ethanol. Approximate molecular weights of the fractions were 500,000 and 60,000. In experiments designed to detect competition for the binding proteins between [(3)H]gibberellin A(1) and closely related [(3)H]gibberellin molecules, [(3)H]gibberellin A(8) and pseudo [(3)H]gibberellin A(1) were inactive, but keto [(3)H]gibberellin competed favorably. Equilibrium dialysis experiments revealed that both high-molecular-weight and intermediate-molecular-weight protein-hormone complexes could undergo hormone exchange with nonlabeled gibberellin A(1).

Chromatography, Gel↗
PubMed1974

Dual effects of ethylene on potato dormancy and sprout growth.

Dormant potato tubers (Solanum tuberosum L.) of two cultivars were treated with various concentrations of ethylene gas for various exposure periods. As has been shown by others, ethylene caused a rapid but transient increase in respiration rate, which appeared to be independent of any effects on dormancy. All concentrations tested caused accelerated sprouting, 2 microliters per liter being the most effective. Ethylene exerts a dual effect on potato tubers: it markedly shortens the duration of rest, but it inhibits elongation of the sprouts during extended treatment. Comparing these results with published work on seeds, bulbs, and corms suggests that ethylene must have a significant but as yet unexplained role in rest and dormancy. However, since the most effective ethylene treatment did not equal the response elicited by treatment with ethylene chlorhydrin, other factors must also contribute to termination of rest.

Journal Article↗
PubMed1974

An amphoteric conjugate of [h]gibberellin a(1) from barley aleurone layers.

The major metabolite produced during incubation of [(3)H]gibberellin A(1) ([(3)H]GA(1)) with barley aleurone layers is an amphoteric, water-soluble compound tentatively called [(3)H]ampho GA(1). Formation of [(3)H]ampho GA(1) in barley aleurones begins after a period of 2.5 hours. As judged by degradation studies as well as Sephadex column chromatography, GA(1) appears to be linked to a peptide; positions C-3 and C-7 were ruled out as conjugation sites.

Journal Article↗
PubMed1973

Effect of Abscisic Acid on Uptake and Metabolism of [H]Gibberellin A(1) and [H]Pseudogibberellin A(1) by Barley Half-seeds.

Uptake and metabolism of 1,2-[(3)H]gibberellin A(1) ([(3)H]GA(1), I) and its 3-hydroxy epimer ([(3)H]pseudoGA(1), II) by barley (Hordeum vulgare L.) half-seeds were measured after 24 hours of incubation, in the presence or absence of abscisic acid in the media. Uptake of both compounds was enhanced by abscisic acid, and abscisic acid enhanced the extent of metabolism of [(3)H]GA(1). However, [(3)H]pseudoGA(1) was not metabolized, even in the presence of abscisic acid. The significance of the stereo-chemistry of the 3-hydroxyl position is discussed.

Journal Article↗