/pdf/biosynthesis-and-mode-of-action-of-lantibiotics-4ckj6jz79p.pdf

Biosynthesis and mode of action of lantibiotics.

CHAPTER 30 – Analysis of Tissues and Body Fluids for Nitrogenous Constituents

Publisher Summary This chapter deals with the chemistry of keratins. The chapter discusses the efforts to prepare pure keratin derivatives for composition, sequence, and end group studies and to obtain mono disperse solutions of these derivatives for physicochemical characterization. It also explores that because the chemistry of keratins has been reviewed, a considerable effort has been made to obtain a better understanding of the complex chemical composition and molecular architecture of these tissues. The natural insolubility of keratins is an obstacle in applying the methods of protein chemistry to them. The chapter reflects the emphasis on wool as a source of α-keratin and is largely confined to a description of progress in the study of this material. This chapter concludes by discussing the histological components of keratin fibers.

The Chemistry of Keratins

Publisher Summary This chapter discusses the chemical aspects of proteins. The problems involved in studying the behavior of any of the functional groups in proteins are great. The minimum requirements appear to to be a full understanding of methods of analysis and of the properties of the groups in simple molecules. The chapter deals with the methods of estimation of thiols, disulfides, and total sulfur. It explores the capabilities and the limitations of the different methods, as well as the reactions of simple thiols, disulfides, and thioethers. The chapter also discusses the sulfur chemistry of a number of proteins. It is concerned with the behavior of SH and SS groups as little work has yet been done on the chemistry of methionine in proteins. The differences in reactivity of SH and SS groups, which occur are discussed and some tentative conclusions are drawn as to the possible functions of these groups. The symbols “SH” and “SS” have been used, when referring to the groups themselves. The words “thiol” and “disulfide” refer to the compounds containing SH or SS groups.

The sulfur chemistry of proteins.

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.

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S.J. Ringel

Papers

Isolation of a new sulfur-containing amino acid (lanthionine) from sodium carbonate-treated wool

Isolation of mesolanthionine from various alkali-treated proteins.

The methionine and cystine content of hen's eggs.

ISOLATION OF dl-LANTHIONINE FROM VARIOUS ALKALI-TREATED PROTEINS