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D D Thomas

Publications and source records attributed to D D Thomas.

196 records · Page 11Linked to original sources
PubMed1977

The diguanosine nucleotides: do they exist in aquatic fungi?

The aquatic fungi Achlya ambisexualis and Blastocladiella emersonii were grown in the presence of 32Pi and the 32P-labeled acid-soluble nucleotide fractions were analyzed by ion-exchange chromatography on DEAE-cellulose. Selected column fractions containing diguanosine tri- and tetra-phosphates (Gp3G and Gp4G) added as chromatographic markers were analyzed further for 32P by chromatography and (or) enzyme hydrolysis. The results of these experiments clearly indicate that neither Gp4G nor Gp3G is synthesized during vegetative growth of these organisms and cast doubt on the hypothesis that diguanosine nucleotides are important metabolic regulators in fungi.

Blastocladiella↗
PubMed1975

The quantitative measurement of rotational motion of the subfragment-1 region of myosin by saturation transfer epr spectroscopy.

According to current models of muscle contraction (Huxley, H. E., Science 164: 1356-1366 [1969]), motion of flexible myosin crossbridges is essential to the contractile cycle. Using a spin-label analog of iodoacetamide bound to the subfragment No. 1 (S1) region of myosin, we have obtained rotational correlation times (tau 2) for this region of the molecule with the ultimate goal of making quantitative measurements of the motion of the crossbridges under conditions comparable to those in living, contracting muscle. We used the newly developed technique of saturation transfer electron paramagnetic resonance spectroscopy (Hyde, J.S., and Thomas, D.D., Ann. N.Y. Acad Sci. 22:680-692 [1973]), which is uniquely sensitive to rotational motion in the range of 10(-7)-10(-3) sec. Our results indicate that the spin label is rigidly bound to S1 (tau 2 for isolated S1 is 2 X 10(-7) sec) and that the motion of the label reflects the motion of the S1 region of myosin. the value of tau 2 for the S1 segment of myosin is less than twice that for isolated S1, while the molecular weights differ by a factor of 4, indicating flexibility of myosin in agreement with the conclusions of Mendelson et al. (Biochemistry 12:2250-2255 [1973]). Adding F-actin increses tau 2 in either myosin or isolated S1 by a factor of mearly 103, indicating rigid immobilization of S1 by actin. Formation of myosin filaments (at an ionic strength of 0.15 or less) increses tau 2 by a factor of 10-30, depending on the ionic strength, indicating a decrease of the rotational mobility of S1 in these agregates. The remaining motion is at least a factor of 10 faster than would be expected for the filament itself, suggesting motion of the S1 region independent of the filament backbone but slower than in a single molecule. F-actin has a strong immobilizing effect on labeled S1 in myosin filaments (in 0.137 M KC1), but the immobilization is less complete than that observed when F-actin is added to labeled myosin monomers (in 0.5 M KC1). A spin-label analog of maleimide, attached to the SH-2 thiol groups of S1, is immobilized to a much lesser extent by F-actin than is the label on SH-1 groups. The maleimide label also was attached directly to F-actin and was sufficiently immobilized to suggest rigid binding to actin.

Actins↗
PubMed1975

Motion of subfragment-1 in myosin and its supramolecular complexes: saturation transfer electron paramagnetic resonance.

Molecular dynamics in spin-labeled muscle proteins was studied with a recently developed electron paramagnetic resonance (EPR) technique, saturation transfer spectroscopy, which is uniquely sensitive to rotational motion in the range of 10(-7)-10(-3) sec. Rotational correlation time (tau2) were determined for a spin label analog of iodoacetamide bound to the subfragment-1 (S-1) region of myosin under a variety of conditions likely to shed light on the molecular mechanism of muscle contraction. Results show that (a) the spin labels are rigidly bound to the isolated S-1 (tau2 = 2 x 10(-7) sec) and can be used to estimate values of tau2 for the S-1 region of the myosin molecule; (b) in solutions of intact myosin, S-1 has considerable mobility relative to the rest of the myosin molecule, the value of tau2 for the S-1 segment of myosin being less than twice that for isolated S-1, while the molecular weights differ by a factor of 4 to 5; (c) in myosin filaments, tau2 increases by a factor of only about 10, suggesting motion of the S-1 regions independent of the backbone of the myosin filament, but slower than that in a single molecule; (d) addition of F-actin to solutions of myosin or S-1 increases tau2 by a factor of nearly 10(3), indicating strong immobilization of S-1 upon binding to actin. Saturation transfer spectroscopy promises to provide an extremely useful tool for the study of the motions of the crossbridges and thin filaments in reconstituted systems and in glycerinated muscle fibers.

Binding Sites↗
PubMed1973

Characteristics and purification of PRR1, an RNA phage specific for the broad host range Pseudomonas R1822 drug resistance plasmid.

A new drug resistance plasmid-dependent RNA containing phage resembling coliphage f2 in its particle size and density is described. The phage, PRR1, will only productively infect some R(+) hosts containing the Pseudomonas drug resistance plasmid R1822. The membrane filter-salt elution patterns, RNase sensitivity, inactivation in low ionic strength solutions, and host range serve to distinguish PRR1 from coliphage f2 and two other Pseudomonas RNA phages, 7s and PP7.

Bacteriophages↗