The effect of urea on various ornithine cycle enzymes has been investigated. It was demonstrated that argininosuccinate lyase was the only ornithine cycle enzyme inhibited by urea in a competitive manner. Based on the data presented the possible role of urea in maintaining a physiological range of intracellular and extracellular urea concentration by controlling hepatic ureogenesis was discussed.

The role of basic amino acids in male infertility is discussed. The changes in the arginine, ornithine and total amino acid concentrations of the seminal plasma in various types of pathospermia are commented upon in the light of published evidence and of the authors' own observations. A recent procedure (CV-technique) introduced by the authors into the routine investigation scheme of infertility is reported. The method detects the arginine-deficient type of pathospermia, thus contributing to the possibility of its selective correction.

Sephadex G-25 (SG-25) chromatography of normal and uremic (U) sera yielded three (A, B, C) optically active (280 nm) fractions. Only fraction B disclosed a substantial increase in uremia that could not be counteracted by routine hemodialysis. Although middle molecules (MM) might be included in all SG-25 fractions (B > C > A), none of them was exclusively composed of MM. Solutes in U fraction B and C were found to be (a) heat stable; (b) soluble in ethanol; (c) diffusible through a Visking membrane, and (d) adsorbed by activated charcoal. Solutes in U fraction B and C and those in a toxic ethanol U serum extract could be partially or entirely recovered in the same Dowex fractions which were obtained by Dowex chromatography of native U sera. Methodical pitfalls leading to misinterpretation of molecular weight data obtained by SG chromatography and to erroneous classification of MM are also thoroughly discussed in this paper.

We describe a new method for measurement of guanidinosuccinate in serum and urine. To separate it from interfering guanidino compounds, it is adsorbed on and eluted from an anion-exchange column. The modified method requires less serum and is considerably faster than previous ones.