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W F Loomis

Publications and source records attributed to W F Loomis.

At least 145 records · Page 8Linked to original sources
PubMed1973

Mutations affecting N-acetylglucosaminidase in Dictyostelium discoideum.

A procedure for screening several thousand clones for alterations in a specific gene product was apapplied to mutagenized cultures of Dictyostelium discoideum. Six strains were recovered which had less N-acetylglucosaminidase (EC 3.2.1.30) than the wild type. In addition, we isolated four strains in which the enzyme was temperature-sensitive. The enzyme from one of these strains had an altered substrate affinity.N-Acetylglucosaminidase is present at a low level in cells grown on bacteria and increases up to 10-fold during the aggregation stage of development. The enzyme appears to be essential to maintain migrating pseudoplasmodia of normal size, as shown by the fact that all of the mutant strains which accumulate very little N-acetyl-glucosaminidase formed only small migrating pseudoplasmodia containing less than 10% the number of cells found in the wild-type pseudoplasmodia. The small pseudoplasmodia migrated at less than a third the rate of wild-type pseudoplasmodia and ultimately formed diminutive fruiting bodies. N-Acetylglucosaminidase thus appears to be a developmental enzyme that functions during the migration stage.

Acetamides↗
PubMed1973

Temperature-sensitive variants of an established myoblast line.

Upon reaching confluency, mononucleated myoblasts fuse into multinucleated myotubes and concomitantly accumulate various characteristic muscle proteins, including myosin, actin, and several enzymes. We have approached the problem of determining the relationship between morphological and biochemical differentiation of muscle cells by isolating a series of temperature-sensitive clones from the established myoblast line, L(6). Twelve phenotypically variant clones were isolated from mutagenized populations of myoblasts. These fell into five classes, distinguishing conditional growth variants from conditional developmental variants. The phenotype of these strains, at least for the more extensively studied ones, was stable for more than 80 generations. Synthesis of characteristic proteins such as myosin, glycogen phosphorylase (EC 2.4.1.1), and phosphocreatine kinase (EC 2.7.3.2) has been studied in two conditional developmental mutants. One mutant, E(3), fuses into myotubes at 37 degrees but not at 40 degrees ; the other, H(6), does not fuse into myotubes at 37 degrees but does so at 40 degrees . At permissive temperatures the enzymes accumulated in mutant cells with the same time course as in the parent cell line. Myosin accumulated in strain E(3) but not in strain H(6). At nonpermissive temperatures neither fusion into myotubes nor accumulation of any of the proteins occured in the cells of these two variant lines.

Animals↗
PubMed1973

Light-induced absorbance changes associated with phototaxis in Dictyostelium.

Reversible light-induced absorbance changes were observed in the phototactic organism Dictyostelium discoideum. Irradiation of cells with light in the 520- to 600-nm region results in an absorbance increase at 411 nm, which decays in darkness with a half-time of about 7 sec. A similar light-induced absorbance change was observed in a 12,000 x g pellet of a cell-free homogenate and in a soluble fraction obtained after sonication of the 12,000 x g pellet. Dithionite had to be added to the cell-free extracts in order for the light-induced change to decay in darkness. The absorbance change was maximally elicited by light in the region of 560 nm. A similar spectral sensitivity was found for the phototactic migration of the pseudoplasmodia. The agreement between the spectral sensitivities of the two processes suggests that the absorbance change is associated with phototaxis.

Cell-Free System↗
PubMed1973

Vestigial DNA?

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Animals↗
PubMed1970

Rickets.

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Air Pollution↗
PubMed1970

Developmental regulation of alpha-mannosidase in Dictyostelium discoideum.

The specific activity of alpha-mannosidase (EC 3.2.1.24) has been found to increase more than a thousandfold during development of the cellular slime mold, Dictyostelium discoideum. The enzyme accumulates in both spore and stalk cells. Studies with preferential inhibitors of macromolecular synthesis indicate that accumulation of alpha-mannosidase requires concomitant protein synthesis and prior ribonucleic acid synthesis. Control of the period of synthesis by the overall developmental program is demonstrated in two temporally deranged morphological mutants. alpha-Mannosidase is found in lysosomes of D. discoideum in association with other acid hydrolases which may be involved in metabolism of extracellular polysaccharide.

Chromatography, Thin Layer↗