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A H Simmons

Publications and source records attributed to A H Simmons.

4 recordsLinked to original sources
PubMed1996

Molecular orientation and two-component nature of the crystalline fraction of spider dragline silk.

The molecular origin of the exceptional mechanical properties of spider silk is unclear. This paper presents solid-state 2H nuclear magnetic resonance data from unoriented, oriented, and supercontracted fibers, indicating that the crystalline fraction of dragline silk consists of two types of alanine-rich regions, one that is highly oriented and one that is poorly oriented and less densely packed. A new model for the molecular-level structure of individual silk molecules and their arrangement in the fibers is proposed. These data suggest that it will be necessary to control the secondary structure of individual polymer molecules in order to obtain optimum properties in bio-inspired polymers.

Alanine↗
PubMed1996

Presence of phosphorus in Nephila clavipes dragline silk.

Solid-state 31P-NMR of Nephila clavipes dragline silk indicates the presence of phosphorus in at least two chemically distinct environments. Amino acid analyses of acid-hydrolyzed silk confirm the presence of phosphotyrosine as one of the phosphorus-containing components. The unusual chemical shift (18.9 ppm downfield from 85% H3PO4), proton chemical shift, and acid lability of a second component suggest that it is part of a strained five-membered cyclic phosphate that might be found on a beta-D-ribose. The five-membered cyclic phosphate is not removed from the silk fibers by exhaustive aqueous extraction. It is absent in nascent silk fibroin from the glands, suggesting that its formation is part of the fiber processing that occurs in the ducts leading to the spinnerets. High-resolution NMR spectra of silk dissolved in propionic acid/12 N HCl (50:50 v/v) show five phosphorus sites assigned to phosphorylated tyrosine residues, phosphorylated serine residues, inorganic phosphate, and two hydrolysis products of the cyclic phosphate compound. The observed posttranslational phosphorylation may be important in the processing and modulation of the physical properties of dragline silk.

Animals↗