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1. 1. The purpose of this investigation was to examine the pattern of glycosaminoglycan (mucopolysaccharide) excretion in urine according to age in man. 2. 2. Glycosaminoglycan preparations were isolated from urines of 11 normal males aged from 7 to 86 years, and were investigated by a series of techniques which included susceptibility to hyaluronidases and paper chromatography. 3. 3. In these preparations the proportion of the glycosaminoglycans resistant to testicular hyaluronidase increased with advancing age.

We analysed the methylation of DNA in vivo by the thymus, spleen, and liver of new-born, growing and adult rats after injection of [methyl-3H]methionine. Further we tested methylation of thymus, spleen, and liver DNA of rats after stimulation of DNA synthesis by a single injection of Brucella abortus suspension and after influencing DNA synthesis by the anti-metabolites Aminopterin and Mitomycin. DNA of different sources was isolated, hydrolysed and analysed for the distribution of radioactivity within the single bases by paper chromatography. CH3 incorporation into DNA was distinctly higher when measured after 4 h instead of 1 h after application of the isotope. Growing rats showed a 5-times higher CH3 incorporation per mg DNA of thymus, spleen and liver compared with adult animals. In growing and adult rats, liver DNA attained the highest radioactivity whereas in new-born animals and after stimulation of DNA synthesis by B. abortus, spleen DNA showed the most prominent radioactive incorporation. Paper chromatograms revealed that the rare base 5-methylcytosine always attained the highest radioactive label, especially in the growing rat and when DNA synthesis became stimulated while defending a high dose of B. abortus. During a strong inhibition of DNA synthesis by injecting the antimetabolite Aminopterin the radioactive label of 5-methylcytosine from methionine in thymus and spleen DNA was less diminished in comparison to the diminuation of the corresponding DNA synthesis measured as [14C]orotic acid incorporation. In contrast to this liver DNA showed a strongly increased [14C]orotic acid incorporation and corresponding to this an increased methylation of cytosine to 5-methylcytosine under the influence of Aminopterin. After injection of Mitomycin, methylation of DNA in the liver also increased in contrast to thymus and spleen where it was diminished. It seems to us that DNA methylation follows every kind of alteration in the DNA polymer. Until now it cannot be decided what biological function DNA methylation serves.