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At least 847 records · Page 47Linked to original sources
PubMed1977

Hydrolysis and epimerization kinetics of hetacillin in aqueous solution.

Methods were developed for quantitating epimerization to epihetacillin and hydrolysis to ampicillin in the alkaline degradation of hetacillin, and both rates in deuterium oxide at 35 degrees and in water at various temperatures were determined. In each case, plots of log k for the epimerization against pH or pD yielded straight lines with a positive slope, which verified the first-order dependence on the hydroxide ion or deuteroxide ion. The activation energy of the epimerization process was 21.2 kcal/mole. In aqueous solution at high pH, epimerization rather than conversion to ampicillin represents a major pathway of hetacillin degradation, although the beta-lactam ring of the hetacillin molecule is highly resistant to attack by the hydroxide ion.

Ampicillin↗
PubMed1975

Does myosin-substrate interaction in vitro result in a delocalized conformation change?

The effect of substrate on the far UV (185-250 nm) and near UV (250-325 nm) circular dichroism (CD) of myosin and heavy meromyosin (HMM) was studied. The following results were obtained with the addition of ATP (during various conditions of hydrolysis), ADP, and pyrophosphate: (1) no changes were observed in the far UV CD, (2) ATP and ADP perturbed the near UV CD only at spectral regions below 280 nm coinciding with the regions of their optical activity, (3) the optically inactive pyrophosphate caused no change in the near UV CD, and (4) myosin and HMM gave exactly the same results. These results suggest that myosin-substrate interaction in vitro does not result in a delocalized conformational change.

Adenosine Diphosphate↗
PubMed1978

Physical-chemical studies of spectrin.

In recent years considerable progress has been made in the understanding of the structure and function of the red blood cell membrane. The protein spectrin, of high molecular weight and propensity for self-association, appears to play a major role, in concert with actin, in maintaining the shape and integrity of the membrane. A study of the physical-chemical properties of spectrin, and its size, shape, self-association pattern, and its interaction with other components, leads to a plausible model for the way this protein performs its biological role. The evidence from the structure and interactions of spectrin suggests a structure which is relatively symmetrical yet highly expanded, and which allows extensive, two-dimensional network formation with actin. In these respects, the structure of spectrin is quite different from that of myosin, to which it has often been likened.

Chemical Phenomena↗
PubMed1975

Electron microscopic characterization of Rhizobium bacteriophage 16-6-12 and its isolated deoxyribonucleic acid.

Bacteriophage 16-6-12 of Rhizobium lupini has a long, non-contractile tail and a head which is hexagonal in outline. The tail is 140 nm in length, 11 nm in diameter, and carries a short term fiber. Analysis of the tail structure by optical diffraction indicates that it is of the helical "stacked disc" type. After phenol-extraction from purified particles, the DNA of phage 16-6-12 can circularize in vitro. No significant difference in contour length was observed between the linear (14.34 plus or minus 0.28 mum) and circular (14.44 plus or minus 0.24 mum) forms of molecules. After partial denaturation with alkali an AT-GC-map was constructed, which shows an asymmetric distribution of AT- and GC-rich regions. It is concluded that this phage DNA can circularize due to the presence of cohesive ends and that it is not circularly permuted.

Bacteriophages↗