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Coatings are among the most ancient technologies of humankind. Relatively soft coatings comprising organic materials such as blood, eggs, and extracts from plants were in use more than 20,000 years ago, and coating activity has been continuously practiced since then with gradually improving materials and application techniques. The fundamental purposes of protecting and/or decorating substrates have remained ubiquitous across all the centuries and cultures of civilization. This article attempts to extrapolate the long tale of change in soft coating technology from its current state by identifying some key problems that attract research and development efforts as our 21st century begins.

The purpose of this study was to determine the safety and efficacy of a live Salmonella choleraesuis immunizing strain, obtained by repeated ingestion and recovery through porcine neutrophils. The strain was tested in mice and in pigs. The vaccine was safe and effective in controlled experimental trials, using clinical, pathologic, and microbiologic criteria. Vaccinated pigs were able to maintain normal weight gains during the 4-week observation period following challenge inoculation with a high dose of a virulent strain.

A method for nonspecifically labeling essentially all exposed residues of a protein is described. A reactive aryl nitrene is generated from N-(4-azido-2-nitrophenyl)-2-aminoethylsulfonate (NAP-Taurine), within 500 mus by flash photolysis in the presence of protein. The reactive nitrene is inserted in about 2 ms into those carbon-hydrogen bonds of the protein that are exposed to the solvent. The method is applied here to ribonuclease A to demonstrate the different degree of labeling of the native and denatured protein. On the basis of amino acid analysis, it appears that residues of the native protein that are buried in the interior of the molecule (as judged from the x-ray structure) do not react with the nitrene. However, when these residues (even nonreactive ones such as valine and proline) are exposed by denaturation of the protein, they do react with the nitrene. It is shown that native ribonuclease A retains 90% of its enzymatic activity when flashed in the absence of NAP-Taurine. This small loss in activity arises from the disruption of a limited portion of the native enzyme structure, as judged by circular dichroism, ultraviolet, and Raman spectra. The site of this limited disruption may be a portion of the enzyme surface near the Cys-26-Cys-84 disulfide bond. The utility of this surface labeling technique for studying the pathways of protein folding or unfolding is discussed.

The steady-state kinetics of the reaction of ribonuclease A with cyclic cytidine 2',3'-phosphate as substrate are investigated as a function of temperature at pH 5 and ionic strength 0.1 M. The results suggest, but cannot prove, that a conformational change near 32 degrees C is involved in the rate-limiting step of the reaction mechanism. This conformational change is proposed to be the same one that was observed in studies of the free enzyme and of enzyme-inhibitor complexes near the same temperature.