The mechanical denaturation process of silk fibroin is examined by Raman spectroscopy. The fresh silk fibroins from the middle gland of mature silkworms are drawn to various ratios on a tensile tester ( R = ldrawn/ linitial, where l is length) and their conformations are measured with Raman spectroscopy. Undrawn silk fibroin is mainly in the random coil structure with some α-helical conformation, the characteristic bands appearing at 1252 and 1660 (random coil) and at 942, 1106, and 1270 cm−1 (α-helix). When the samples are drawn up to R = 4 at an extension rate of 500 mm/min, two peaks at 1233 cm−1 (the amide III band) and 1085 cm−1 appear; it is shown that the β-sheet conformation is then formed. With an increase in drawing ratios, the intensities of these β-sheet bands increase and those of the random coil and α-helical bands decrease gradually. These changes indicate that, under the action of stress, the conformation of fibroin is altered from random coil and α-helix to β-sheet structures. This result is quite similar to the results achieved by the spinning of the silkworm. The effect of the water content in liquid silk on this conformational transition process is revealed and discussed.

Amelogenins, a class of sparsely phosphorylated hydrophobic proteins characterized by a high concentration of Pro, Gln, Leu, and His have been implicated in the mineralization of tooth Recently a unique primary structure of bovine tooth enamel amelogenin was reported by Takagi et al.,3 characterized by repeating tripeptides Gln-Pro-X near the C-terminal region. Recent CD, Fourier transform infrared, and Chou-Fasman predictions of the secondary structure4 of the lower molecu- Lagant et al.7.' and Krimm and Seaton (see Refs. 9 and 10, and other references cited therein). In addition, Raman spectra provide information on the side-chain conformations of certain aromatic amino acid residues. EXPERIMENTALPreparation of the major highest molecular weight bovine amelogenin from developing premolar teeth has been previously de~cribed.~ Raman spectra were obtained with a Spex Industries Ramalog 5 Raman spectrometer equipped with the computer Spex SCAMP. A sample of amelogenin in aqueous solution was placed in a capillary tube and was illuminated using the 514.5-nm excitation line of an argon-ion laser (Spectraphysics model SP-164). A green interference filter was used to eliminate plasma lines of the laser. The signal was averaged from 10 scans by SCAMP data acquisition processor. Deuterated amelogenin was made by dissolving amelogenin in D,O and then by lyophilization to recover the solid. The sample was again dissolved in D,O for

A gallstone from Egypt was examined by laser Raman spectroscopy and identified to be a bilirubin-type stone. The surface of the stone, the subsurface interior, and the center of the stone were irradiated with the 514.5-nm argon-ion laser line. Spectra from the three areas gave similar Raman spectral patterns. Moreover, Raman spectra from the interior of the gallstone were identical to that of bilirubin standard. However, the examination of a Raman spectrum from the outer surface of the stone indicated that it contained cholesterol in addition to bilirubin. Bilirubin has the characteristic line of C=C stretching vibration at 1615 cm−1. Cholesterol has the characteristic line of C(5)=C(6) stretching vibration at 1674 cm−1. Cholesterol also has a strong characteristic line at 1439 cm−1. Therefore, it is quite easy to identify the constituents of gallstone by Raman spectroscopy.

Two hemorrhagic proteases, Lachesis hemorrhagic toxins a and b (LHTa and LHTb), were isolated from the venom of Lachesis muta, which is distributed in Central and South America. One protease showed strong hemorrhagic action, while the other showed weak hemorrhagic activity even though the two enzymes are very similar in their chemical properties. Neither enzyme hydrolyzed arginine esters, but both hydrolyzed casein and reduced fibrinogen. The A alpha chain of fibrinogen was hydrolyzed first, and the B beta chain was hydrolyzed later. The gamma chain of fibrinogen was resistant to hydrolysis. The molecular weights of LHTa and LHTb were very similar, 22,000 and 23,000, respectively. The amino acid composition of LHTa was also similar to that of LHTb. The secondary structure of LHTa as determined by Lippert's equation was 52% alpha helix, 17% beta sheet, and 31% random coil; that of LHTb was 47% alpha helix, 13% beta sheet, and 40% random coil.

This study was conducted to characterize surface layer cracking in Vertisols by determining surface displacement trends. A disturbed sample from the Ap horizon of a Randall clay (fine, smectitic, thermic Ustic Epiaquerts) was evaluated. Digital image correlation (DIC) used to track the movement of points on the surface as the soil dried and to assess the development of soil surface cracking. Displacement fields among a group of images were obtained by using a cross‐correlation algorithm. The displacement vectors resulting from the analysis of the displaced fields can be used to show cracking patterns on a ground‐up soil sample from a Vertisol before they become visually apparent. Digital image correlation may be used to calculate the deformation of the surface layer with relatively high precision.