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M Flashner

Publications and source records attributed to M Flashner.

46 records · Page 3Linked to original sources
PubMed1978

Effects of cytochalasin A on the morphology of plasmodia and sclerotia of Physarum polycephalum.

Cytochalasin A (CA) at 1.6 X 10(-5)M and lower concentrations produced disruptive effects upon plasmodia, sclerotia, and spherule forms of Physarum polycephalum. CA effects upon either micro- or macroplasmodia included: cytoplasmic condensation, plasmodial contraction, and scission at the plasma membrane. The latter manifestation was most dramatically observed by scanning electron microscopy. Electron microscopy of drug-treated palsmodia confirmed the above phase contrast light-microscopic results and revealed, in addition, vacuolar enlargement, decreased membrane invaginations, and the presence of condensed particles within the plasmodium and at the plasma membrane. These results of drug action were not reversed by washing of exposed plasmodia. Germination of the slcerotial and spherule forms of Physarum was CA-delayed by 12 and 96 hours, respectively. Approximately 10% of drug-treated sclerotia were found to have been burst apart. These dramatic CA effects were nullified by preincubation of the drug either with L-cysteine or with beta-mercaptoethanol; however, iodoacetamide (10(-6)M) gave no such morphologic consequences. Cytochalasins B or D at comparable concentrations were without activity. It is concluded therefore that CA effects upon the myoxomycete reflect specific acceptor responses.

Cysteine↗
PubMed1977

Properties of an inducible extracellular neuraminidase from an Arthrobacter isolate.

The elective isolation of a soil microorganism, tentatively assigned to the genus Arthrobacter, which produced an extracellular neuraminidase is described. The secretion of neuraminidase from washed cells in minimal medium required the presence of sialo-containing glycoproteins, whereas free N-acetyl-neuraminic asid of N-acetylmannosamine were poor inducers. No enzyme could be dected in the induction fitrated of cells, in the absence of inducer or in the culture filtrate of cells grown in a complete medium. The routine enzyme inducer was a hot-water extract of "edible bird's nest." Mild acid treatment (0.05 N H2SO4) of this extract increased enzyme activity two--to threefold and the specific activity about eightfold. Neuraminidase induction with acid-treated bird's nest was manifested at a linear rate for 6 h without increase in cell number. No other anticipated glycohydrolase or protease activities were foud. The amount of enzyme located within the cells was barely detectable as compared to that found in the induction filtrate. Experiments with chloramphenicol or chlortetracycline indicate that de novo protein synthesis was required for neuraminidase production and that this exoenzyme was not released from a preformed pool. Neuraminidase from this source has an apparent molecular weight of 87,000, a pH optimum of 5 to 6, and an apparent Km of 2.08 mg/ml for collocalia mucoid and 3.3 X 10(-3) M for N-acetylneuraminlactose and is insensitive both to Ca2+ ions and ethylenediaminetetraacetic acid. Preliminary studies indicate that the enzyme can hydrolyze alpha-2,3-, alpha-2,6-, or alph-2-8-N-acetylneuraminylglycosidic linkages. From total activity data and purification criteria, it would appear that this isolate can produce about 5 mg of enzyme per liter of induction medium.

Arthrobacter↗
PubMed1977

Arthrobacter sialophilus sp. nov.; a neuraminidase-producing coryneform.

A new species of Arthrobacter is described for which the name A. sialophilus is proposed. The organism was obtained by elective culture from soil using Collocalia mucoid, and can readily be induced in replacement minimal media with appropriate substrates, to form the enzyme neuraminidase. It undergoes sphere-rod-sphere morphogenesis, is gram-variable, non-motile, aerobic, catalase-positive, oxidase-negative, fails to release acid or gas from saccharides, has a GC content of 56.0 mol % and can grow at temperatures up to 45 degrees C. The peptidoglycan composition of its spherical form contains neither diaminopimelic acid nor arabinose as components, but does manifest the presence of glycine. Its generation time at 30 degrees C on tryptone-yeast extract medium is 1.6 h. Accessory growth factors do not appear to be required. The organism, though colorless in the dark, provides a bright yellow water-insoluble pigment after exposure to light. The foregoing combination of properties distinguishes this isolate from other well-described Arthrobacter spp.

Arthrobacter↗
PubMed1976

Rabbit muscle pyruvate kinase. Amino- and carboxyl-terminal studies.

Amino-terminal analysis of rabbit muscle pyruvate kinase (ATP:pyruvate 2-O-phosphotransferase, EC 2.7.1.40) failed to detect the presence of any free amino-terminal residues. Acetyl group analysis demonstrated the presence of between 3.7 and 4.0 mol of acetyl groups per mol of enzyme. The acetylated amino-terminal residue was isolated from pronase digests of the enzyme and identified as N-acetylserine. Quantitative recovery experiments indicated that all acetyl residues are found at the amino termini. Carboxyl-terminal analyses using the tritium exchange method suggested the presence of a blocked carboxyl-terminal residue, supporting previous hydrazinolysis and carboxypeptidase studies.

Acetates↗