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Biomedical subjects

M M Allen

Publications and source records attributed to M M Allen.

At least 19 recordsLinked to original sources
PubMed2001

A rapid and sensitive method for the analysis of cyanophycin.

A method has been devised for the quantitative analysis of cyanophycin, based on (1)H nuclear magnetic resonance (NMR) spectroscopy, allowing determination of the nitrogen status of cyanobacteria. Cyanophycin is extracted with minimal washing from small volumes of cells and quantified by integration of the NMR peak attributed to the protons attached to the delta-carbon of arginine. Linear relationships were found between the amount of cyanophycin determined by this method and both known concentrations of cyanophycin solutions and the amount of cyanophycin determined using the standard chemical arginine assay.

Bacterial Proteins↗
PubMed2001

The role of the speech-language pathologist in improving decoding skills.

In this article, we consider the processes and knowledge involved in decoding and present some instructional guidelines and suggestions for teaching students the skills necessary for proficient and fluent word reading. The roles and responsibilities of speech-language pathologists (SLPs) are also considered. It may have been enough several years ago for SLPs to focus solely on early literacy skills and phonological awareness. This is not the case today. SLPs not only need to collaborate with teachers to develop a comprehensive approach to literacy, but also should be providing direct, explicit instruction of decoding skills for students with language and learning disabilities.

Awareness↗
PubMed2000

How adolescents comprehend unfamiliar proverbs: the role of top-down and bottom-up processes.

Typically achieving students who were 12, 15, and 18 years old (n = 150) participated in this investigation. The goal was to determine the extent to which students' prior knowledge of the nouns in unfamiliar proverbs would be associated with their ability to comprehend the expressions and how the relationship between word knowledge and proverb comprehension might change during the developmental period from late childhood to late adolescence. Proverbs containing concrete nouns (e.g., "Two captains will sink a ship") (concrete proverbs) and those containing abstract nouns (e.g., "Envy is destroyed by true friendship") (abstract proverbs) were presented in a multiple-choice task designed to examine comprehension of the expressions. Knowledge of the relevant semantic features of each noun was examined in a separate multiple-choice task. Word knowledge was found to be associated with proverb comprehension in all groups--and particularly so in the case of abstract proverbs. The results support a model of proverb comprehension in adolescents that includes bottom-up in addition to top-down processes.

Adolescent↗
PubMed1999

NMR study of the metabolic 15N isotopic enrichment of cyanophycin synthesized by the cyanobacterium Synechocystis sp. strain PCC 6308.

1H, 13C and 15N nuclear magnetic resonance (NMR) spectroscopy has been used to characterize cyanophycin, a multi-l-arginyl-poly-[l-aspartic acid] polypeptide from the cyanobacterium Synechocystis sp. strain PCC 6308. 1H, 13C and 15N chemical shifts and 1JHN and 1JCN coupling constants were measured in isolated 15N-labeled cyanophycin, and showed chemical shift values and J-couplings consistent with the reported polypeptide structure. 15N enrichment levels were determined from the extent of 1H-15N J-coupling in 1H NMR spectra of cyanophycin. Similar experiments using 13C-15N coupling in 13C NMR spectra were not useful in determining enrichment levels.

Bacterial Proteins↗
PubMed1998

Two internal pools of soluble polyphosphate in the cyanobacterium Synechocystis sp. strain PCC 6308: an in vivo 31P NMR spectroscopic study.

Two intracellular pools of soluble polyphosphate were identified by in vivo 31P NMR spectroscopy in the cyanobacterium Synechocystis sp. strain PCC 6308. Polyphosphate was present in the cells after growth in sulfur-limited media containing excess phosphate. The presence of polyphosphate was confirmed by transmission electron microscopy and chemical analysis. 31P NMR spectroscopy of whole cells treated with EDTA revealed two pools of mobile polyphosphate. A downfield shift and narrowing of part of the broad polyphosphate resonance was observed after EDTA treatment, suggesting that EDTA binds metal ions normally associated with some of the polyphosphate. Phosphate, but not polyphosphate, leaked out of the cells after this treatment. Addition of magnesium ions caused the downfield shift in the polyphosphate resonance to move back toward its original value. These data show that only part of the cation-complexed polyphosphate is accessible to the added EDTA and suggest that there are two internal fractions of NMR-visible polyphosphate in the cells, only one of which loses its associated cations to EDTA. Spheroplast formation showed that polyphosphate was not present in the periplasm of the cells.

Cyanobacteria↗
PubMed1997

31P NMR identification of metabolites and pH determination in the cyanobacterium Synechocystis sp. PCC 6308.

The identity of a number of phosphorus-containing metabolites present in Synechocystis sp. PCC 6308 has been confirmed by 31P NMR spectroscopy. The presence of D-ribulose 1,5-bisphosphate (RuBP); DL-glyceraldehyde 3-phosphate (GlyP); D(-)3-phosphoglyceric acid (3PGA); D-ribulose 5-phosphate (Ru5P);6-phosphogluconic acid (6PGA); phosphoenolpyruvate (PEP); inorganic phosphate (Pi); uridine diphosphoglucose (UDPG); ADP and ATP were demonstrated by the pH dependence of their 31P NMR chemical shifts in spectra of perchloric acid cell extracts. Intracellular pH of cells was determined to be 7.5-7.7.

Adenosine Diphosphate↗
PubMed1994

Variations in the amino acid composition of cyanophycin in the cyanobacterium Synechocystis sp. PCC 6308 as a function of growth conditions.

Gas chromatography-mass spectrometry studies of the nitrogen isotopic composition of the N-trifluoroacetyl n-butyl ester derivatives of the amino acids from isolated hydrolyzed cyanophycin from 15N-enriched cells led to two major findings: (1) the amino acid composition of this granular polypeptide, isolated using procedures optimized for extracting and purifying cyanophycin from cells in the stationary growth phase, varied with the culture growth condition; (2) the rate of incorporation of exogenous nitrate differed for each nitrogen atom of the amino acid constituents of cyanophycin or cyanophycin-like polypeptide. Arginine and aspartic acid were the principle components of cyanophycin isolated from exponentially growing cells and from light-limited stationary phase cells, with glutamic acid as an additional minor component. The cyanophycin-like polypeptide from nitrogen-limited cells contained only aspartic and glutamic acids, but no arginine. The glutamic acid content decreased and arginine content increased as nitrate was provided to nitrogen-limited cells. These cells rapidly incorporated nitrate at different rates at each cyanophycin nitrogen site: guanidino nitrogens of arginine > aspartic acid > alpha-amino nitrogen of arginine > glutamic acid. Little media-derived nitrogen was incorporated into cyanophycin of exponentially growing cells during one cellular doubling time.

Amino Acids↗
PubMed1990

Effect of Nitrogen Starvation on Polypeptide Composition, Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase, and Thylakoid Carotenoprotein Content of Synechocystis sp. Strain PCC6308.

Synechocystis sp. strain PCC6308 cells were starved for nitrogen for 5 days. The polypeptide compositions of whole cell extracts and washed membranes of nitrogen-replete and nitrogen-starved cells were compared by one- and two-dimensional electrophoresis. Immunoblotting of one-dimensional gels indicated that pelletable ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) was depleted in cells starved for nitrogen, while levels of soluble Rubisco were comparable in nitrogen-starved and nitrogen-replete cells. This is consistent with the hypothesis that pelletable Rubisco may serve as a nitrogen reserve in Synechocystis 6308. Other polypeptides were differentially enriched in the membrane or soluble fractions of nitrogen-replete cells or nitrogen-starved cells, suggesting nitrogen starvation may alter partitioning of polypeptides into soluble and membrane fractions. Degradation of abundant polypeptides during nitrogen starvation appeared to cause an effective magnification of less abundant polypeptides in the molecular mass range of 20 to 40 kilodaltons, as shown by two-dimensional electrophoresis. A 42-kilodalton thylakoid carotenoid protein identified by immunoblotting was conserved in membranes from nitrogen-starved cells. This may be functional for cells depleted of pigment and thus exposed to higher light levels because of decreased self-shading.

Journal Article↗
PubMed1989

Changes in polypeptide composition of Synechocystis sp. strain 6308 phycobilisomes induced by nitrogen starvation.

Phycobilisomes isolated from actively growing Synechocystis sp. strain 6308 (ATCC 27150) consist of 12 polypeptides ranging in molecular mass from 11.5 to 95 kilodaltons. The phycobilisome anchor and linker polypeptides are glycosylated. Nitrogen starvation causes the progressive loss of phycocyanin and allophycocyanin subunits with molecular masses between 16 and 20 kilodaltons and of two linker polypeptides with molecular masses of 27 and 33 kilodaltons. Nitrogen starvation also leads to enrichment of four additional polypeptides with molecular masses of 46, 53, 57, and 61 kilodaltons and a transient enrichment of 35- and 41-kilodalton polypeptides in isolated phycobilisomes. The 57-kilodalton additional polypeptide was identified by immunoblotting as the large subunit of ribulosebisphosphate carboxylase/oxygenase. Proteins with the same molecular weights as the additional polypeptides were also coisolated with the 12 phycobilisome polypeptides in the supernatant of nitrogen-replete Synechocystis thylakoid membranes extracted in high-ionic-strength buffer and washed with deionized water. These observations suggest that the additional polypeptides in phycobilisomes from nitrogen-starved cells may be soluble or loosely bound membrane proteins which associate with phycobilisomes. The composition and degree of association of phycobilisomes with soluble and adjacent membrane polypeptides appear to be highly dynamic and specifically regulated by nitrogen availability. Possible mechanisms for variation in the strength of association between phycobilisomes and other polypeptides are suggested.

Blotting, Western↗
PubMed1983

Effects of Photosystem II Herbicides on the Photosynthetic Membranes of the Cyanobacterium Aphanocapsa 6308.

The effects of the photosystem II herbicides diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea) and atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) on the photosynthetic membranes of a cyanobacterium, Aphanocapsa 6308, were compared to the effects on a higher plant, Spinacia oleracea. The inhibition of photosystem II electron transport by these herbicides was investigated by measuring the photoreduction of the dye 2,6-dichlorophenol-indophenol spectrophotometrically using isolated membranes. The concentration of herbicide that caused 50% inhibition of electron transport (I(50) value) in Aphanocapsa membranes for diuron was 6.8 x 10(-9) molar and the I(50) value for atrazine was 8.8 x 10(-8) molar. (14)C-labeled diuron and atrazine were used to investigate herbicide binding with calculated binding constants (K) being 8.2 x 10(-8) molar for atrazine and 1.7 x 10(-7) molar for diuron. Competitive binding studies carried out on Aphanocapsa membranes using radiolabeled [(14)C]atrazine and unlabeled diuron revealed that diuron competed with atrazine for the herbicide-binding site. Experiments involving the photoaffinity label [(14)C]azidoatrazine (2-azido-4-ethylamino-6-isopropylamino-2-triazine) and autoradiography of polyacrylamide gels indicated that the herbicide atrazine binds to a 32-kilodalton protein in Aphanocapsa 6308 cell extracts.

Journal Article↗
PubMed1983

Protein degradation and synthesis of cyanophycin granule polypeptide in Aphanocapsa sp.

Cyanophycin granule polypeptide content increased by 2- to 3-fold, soluble protein content decreased by 1.5-fold, and carbohydrate content increased by 2-fold within 6 h of chloramphenicol addition to exponentially growing cells of Aphanocapsa sp. strain 6308. Analysis of 14C- and 3H-labeled cells transferred to unlabeled medium and analysis of pulse-labeled cells both suggested cyanophycin granule synthesis from preformed protein breakdown.

Arginine↗
PubMed1980

Cyanophycin granule polypeptide formation and degradation in the cyanobacterium Aphanocapsa 6308.

The effect of a number of conditions on the amount of cyanophycin granule polypeptide [multi-L-arginyl poly(L-aspartic acid)] formed in the unicellular cyanobacterium Aphanocapsa 6308 was determined. Light, CO2, sulfur, and phosphorus starvation as well as the addition of arginine to culture media increased the amount of cyanophycin granule polypeptide in cells when compared with that in cells grown under conditions optimal for growth. Nitrogen limitation and reduction of growth temperature to 30 degrees C decreased the amount of cyanophycin granule polypeptide on a dry-weight basis. Shift-up and shift-down experiments suggest cyanophycin granule polypeptide may be a reserve nitrogen polymer in Aphanocapsa 6308.

Arginine↗
PubMed1980

Structure and composition of cyanophycin granules in the cyanobacterium Aphanocapsa 6308.

Cyanophycin granules in the unicellular cyanobacterium Aphanocapsa 6308 were examined with the electron microscope in both thin section and by freeze-fracture techniques. Purified granules were examined with the electron microscope, by arginine determinations, by chromatography, and by elemental analysis. They are similar in ultrastructure and composition to those isolated from the nitrogen-fixing cyanobacterium Anabaena cylindrica, consisting of equal molar quantities of L-arginine and L-aspartic acid.

Arginine↗
PubMed1978

Comparison of rhapidosomes and asbestos microfibrils.

Rhapidosomers (cylindrical nucleoprotein rods of bacterial origin) show great structural similarity to the microfibrils of chrysotile asbestos when negatively stained and observed with the electron microscope. If the negative stain is omitted, the asbestos retains its structural detail whereas the rhapidosomes appear to be unstructured bodies. When the microscope is adjusted into a selected area diffraction mode, the asbestos shows characteristic electron diffraction patterns whereas the rhapidosomes appear to be amorphous to electron diffraction.

Asbestos↗
PubMed1978

Arginine catabolism in Aphanocapsa 6308.

The catabolic products of arginine metabolism were observed in Aphanocapsa 6308, a unicellular cyanobacterium, by thin layer chromatography of growth media, by limiting growth conditions, and by enzymatic analysis. Of the organic, nitrogenous compounds examined, only arginine supported growth in CO2-free media. The excretion of ornithine at a concentration level greater than citrulline suggested the existence in Aphanocapsa 6308 of the arginine dihydrolase pathway which produced ornithine, CO2,NH4,+ adenosine 5'-triphosphate. Its existence was confirmed by enzymatic analysis. Although cells could not grow on urea as a sole carbon source a very active urease and subsequently an arginase were also demonstrated, indicating that Aphanocapsa can metabolize arginine via the arginase pathway. The level of enzymes for both pathways indicates a lack of genetic control. It is suggested that the arginase pathway provides only nitrogen for the cells wheras the arginine dihydrolase pathway provides not only nitrogen, but also CO2 and adenosine 5'-triphosphate.

Adenosine Triphosphate↗
PubMed1978

Variations in short term products of inorganic carbon fixation in exponential and stationary phase cultures of Aphanocapsa 6308.

Aphanocapsa 6308 metabolizes both NaHCO3 and Na2CO3. The short term incorporation (5-s) metabolic pattern and the patterns of incorporation of bicarbonate for exponential versus stationary phase cultures differ, however. Cells were equilibrated for 10 min in air and distilled water prior to injection of either NaH14CO3 at pH 8.0, or Na214CO3 at pH 11.0. Hot ethanol extracts were analyzed via paper chromatography and autoradiography for products of CO2 fixation. At 5 s, malate (51.5%) predominates slightly as a primary bicarbonate fixation product over 3-phosphoglycerate (40.3%); 3-phosphoglycerate is the primary product of carbonate fixation. At 60 s, the carbonate and bicarbonate labelling patterns are similar. Cells in stationary phase fix in 5 s a greater proportion of bicarbonate into malate (36% vs. 14% for 3-phosphoglycerate) than do cells in exponential growth. Likewise, 60 s incorporations show a large amount of bicarbonate fixed into aspartate (30.9%) in stationary phase cells over that of exponential phase (11.6%). These data suggest an operative C4 pathway for purposes not related to carbohydrate synthesis but rather as compensation for the incomplete tricarboxylic acid cycle in cyanobacteria. The enhancement of both aspartate fixation and CO2 fixation into citrulline in stationary phase correlates with an increase in cyanophycin granule production which requires both aspartate and arginine.

Aspartic Acid↗