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M Goodman

Publications and source records attributed to M Goodman.

At least 505 records · Page 28Linked to original sources
PubMed1971

Conformational transition in oligopeptides: an NMR spectroscopic study.

We examined the 220-MHz NMR spectra for a series of oligopeptides derived from gamma-ethyl L-glutamate, an octapeptide based on beta-methyl L-aspartate, and a low molecular weight L-glutamate polymer ([unk]DP = 20) in deuterochloroform-trichloroacetic acid. A definite transition from folded to nonhelical forms was established for the glutamate systems. The aspartate behavior is explained by a progressive solvation of a peptide chain in a disordered conformation. In all the solvent systems studied, separate peaks for each N-H are observed for the glutamate and aspartate oligomers. Thus, end effects and polydispersity are important in interpreting NMR spectra of partially helical polypeptides. Slow exchange between NH groups on the same chain does not appear to play a significant role in the helix-coil transition.

Aspartic Acid↗
PubMed1971

Salmonella locus affecting phosphoenolpyruvate synthase activity identified by a deletion analysis.

Strain leu-4017, derived from Salmonella typhimurium LT2, cannot utilize acetate, pyruvate, or citric acid cycle intermediates as sole sources of carbon. The mutation in this strain extends from the A cistron of the leucine operon to some point between leu and azi, presumably deleting one or more loci involved in the utilization of these compounds. One of these loci is required for phosphoenolpyruvate synthase activity.

Acetates↗
PubMed1970

Crystal and molecular structure of n,n'-diethyl-n,n'-diphenylurea.

N,N'-diphenyl-N,N'-diethylurea (C(17)H(20)N(2)O) crystallizes in the space group P2(1)/c. The unit cell constants are: a = 10.42 +/- 0.01 A, b = 16.86 +/- 0.02 A, c = 10.66 +/- 0.001 A, beta = 125 degrees 16' +/- 5'; Z = 4, D(x) = 1.16 g.cm(-3), D(meas) = 1.16 +/- 0.01 g.cm(-3). Data for 1392 reflections were collected at room temperature on a Picker automated diffractometer. The crystal structure was solved by direct methods and refined by bloc-diagonalized matrix least-squares calculations. The molecule is characterized by a pseudo C(2) symmetry; both phenyl groups are trans with respect to the oxygen atom. The hybridization of the two nitrogen atoms is intermediate between trigonal and tetrahedral; the nonplanar distortion of the amide groups is about 30 degrees . The amide C-N bond lengths are 1.37 A.

Journal Article↗
PubMed1969

Flexibility of supposed "rigid" molecules: substituted 2,5-piperazinediones (diketopiperazines).

The relevant results of accurate X-ray analyses of both the trans-and the L-cis-3,6-dimethyl-2,5-piperazinediones (diketopiperazines) are reported. We note that a large variability of conformations for the ring system can be accomplished by coupling small bond-angle deformations with large variations of the internal rotation angles. The experimental molecular models are discussed in terms of these changes and in terms of nonbonded intramolecular interactions.

Journal Article↗
PubMed1969

Sensitive criteria for the critical size for helix formation in oligopeptides.

We studied the conformation of a series of gamma-ethyl-L-glutamate oligopeptides by circular dichroism and 220 MHz nuclear magnetic resonance spectroscopy. By use of the first technique we noted enhancement of the n --> pi(*) and splitting of the pi --> pi(*) transitions commencing with the heptamer in trimethylphosphate and trifluoroethanol. With the second method we found changes in chemical shifts for the amide protons consistent with the onset of helicity at the heptamer in the solvents noted above. When DMSO-d(6) is used as a solvent, no such chemical shift changes occur because the oligopeptides do not assume helical conformations.

Magnetic Resonance Spectroscopy↗