410 results provide a general confirmation of the conclusions reached in the preceding papers of this series . Acknowledgment. The authors acknowledge the assistance of John S. Mason in the determination of sol fraction, gel fraction, and distention index; Ines V. I deGruy in the electron micrographic analyses; and George I. Pittman in the preparation of the line drawings. _ . of Reagent Residues in Cotton Cellulose Modified with tris(1-Aziridinyl)phosphine Oxide, Textile Res. J . 40, 395-400 (1970).ABSTRACT A more reproducible method for determining the swelling of wool fibers is suggested. It has been shown that high concentrations of urea do not increase the swelling of wool in cold aqueous solution. The influence of the addition of small amounts of sodium metabisulfite and wetting agents on the swelling of wool in urea solutions is discussed. It has been shown that small amounts of surface protein material are removed from the wool by concentrated urea solutions. The reported presence of a amino adipic acid in the surface material has been confirmed and over-all analysis of the ureasoluble material indicates its similarity with a previously isolated cuticular sheath fraction. The implications of these findings in relation to wool processing are discussed.

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1. Studies have been made with solvent-extracted chicken muscle, bovine plasma albumin (BPA) and other proteins, all severely heated in the absence of carbohydrates so as to cause a large decrease in their fluorodinitrobenzene (FDNB)-reactive lysine contents.2. ɛ-N-(β-L-aspartyl)-L-lysine and ɛ-N-(γ-L-glutamyl)-L-lysine isopeptides were determined after enzymic digestion of heated chicken muscle, and their content was found to increase as the material was subjected to more heat treatment. Heated chicken muscle was not found to contain lanthionine. Heated BPA, on the other hand, was found to contain lanthionine but not the isopeptides. Both lanthionine and isopeptide cross-linkages were detected in most of the other heated proteins. There was some difficulty in quantifying the amounts of isopeptides formed on heat treatment, because the enzymic digestion procedure used in their isolation appeared to be incomplete. Neither lysinoalanine nor ornithinoalanine was detected in any of the test materials.3. The severely heated chicken muscle was fed to rats, and ileal and faecal digestibilities were studied. Protein digestibility was found to be greatly reduced after heat treatment, although the isopeptides themselves appeared to be at least as digestible as the total N component, total lysine, or FDNB-reactive lysine. However, the reduction in ileal N digestibility only partly accounted for the much larger reduction in nutritive value, as measured by net protein ratio ((weight loss of N-free animals + weight gain of test animals) ÷ weight of crude protein (N × 6.25) consumed by test animals). Possible reasons for this are discussed.

Isopeptide links refer to bonds between the &-amino group of lysine and the side-chain carboxyl groups of glutamic or aspartic acid. Covalent crosslinks of this kind, which undoubtedly occur in protein feedstuffsand reduce their nutritional value, also participate In the fibrinogen-tfibrin transformation and play a part in stabilizing the structure of keratins. Isopeptide links also arise on heating of both fibrous and globular proteins, the amount formed depending upon the severity of heat treatment. The mode of formation and the significance of these crosslinks require further elucidation.