Experiments on the theory of photochemical formation of carcinogens from skin fats.
Irradiation products of skin surface fats, including digitonin-precipitable sterols, isocholesterols, and total unsaponifiable fractions, were painted on the ears of white mice for periods of from 15 to 18 months, but failed to produce precancerous or cancerous changes that could be noted histologically. Therefore, the theory of photochemical formation of carcinogenic compounds on the surface of the skin by ultraviolet irradiation could not be substantiated by this method.
Lipids in cancer.
Publisher Summary This chapter discusses that the lipids to which attention has been directed by investigators in cancer are the phospholipids, lecithin, cephalin and sphingomyelin, cholesterol, free and combined as ester, and fat including the constituent fatty acids especially the unsaturated fatty acids. Of the phospholipids, cephalin is regarded as the structural phospholipid while lecithin and probably sphingomyclin are regarded as metabolic. The chapter highlights that most of the combinations of proteins, lipids, and metals are of extremely loose type as compared to the more familiar stable types of compounds. A chemical purity has always made implicit demand that a compound possess types of linkages that are clearly defined by chemical knowledge. The chapter also explores that most of the organs and tissues of the tumor-bearing animal became like the tumor in regard to concentrations of lipids. Exceptions were the brain and the spleen. The adrenals of different animals with a variety of tumors have been studied rather extensively: marked hypertrophy and loss of lipids were the characteristic findings, which have been attributed to adrenal cortical exhaustion.
New method for analysis of enzymatic reactions: Thermolysin-catalyzed synthesis of aspartame precursor
Aspartame is an artificial sweetener which is 200 times sweeter than sucrose. A precursor of aspartame, N-(benzyloxycarbonyl)-l-aspartyl-l-phenylalanine methyl ester (Z-APM) was synthesized and hydrolyzed with thermolysin in an aqueous monophasic system. Graphical plotting methods and/or nonlinear regression have been used to analyze enzymatic reactions because of the nonlinearity of enzymatic rate equations. There are, however, problems: the former require accurate measurement of the initial reaction rate and the latter gives no analytical information. The authors proposed a method to solve the nonlinear enzymatic rate equations with respect to the concentration of a product with the Taylor expansion, especially for the reversible Theorell-Chance mechanism (Murakami, Y., Hirata, M., and Hirata, A., J. Ferment. Bioeng., 82, 246–252, 1996). This solution, however, is complex for practical use. In this paper, a simpler solution to explain the thermolysin-catalyzed synthesis of Z-APM is obtained. New methods to determine the kinetic parameters, especially for the reversible Theorell-Chance mechanism, based on the approximated solution are proposed. The results calculated using the obtained kinetic parameters can satisfactorily explain the experimental results, which demonstrates the effectiveness of the proposed analysis. We must know the relation between the concentrations of substrates and a product, and accurately evaluate of the result obtained using Taylor expansion when we determine the kinetic parameters using our newly developed methods. The methods to determine the kinetic parameters of the reversible Theorell-Chance mechanism described in this paper is, however, expected to be applied to general enzymatic reactions.