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The synthesis of hepatic catalase in normal and S.180 bearing mice at different times after tumor implantation was studied by injection of 59Fe and successive isolation of cytoplasm proteins. On the basis of several control experiments the presence of ferro-proteins other than catalase in the isolated material was excluded. In a series of experiments with mice bearing 5 days tumors, the catalasic activity appeared already reduced, the radioactive iron incorporation on the contrary was increased. In a second series, where mice with 10 and 15 days tumors were used, the depression of catalase activity was very evident. The radioactive iron incorporation was proportionally much more reduced, and sometimes almost abolished. It is concluded that the tumor induces first an increase of the rate of destruction, and later a block of the hepatic catalase synthesis.

As an introduction to a series of papers on tumor substances inhibiting the activity of liver catalase, a critical review of the present situation of the general problem about the inhibition of this enzyme in tumor-bearing organisms is outlined. Data from researches carried out in order to determine the nature of the inhibitors are then exposed. « Toxohormone » was prepared from, human and experimental tumors and from ascitic fluids. It has been observed that, by the methods usually employed for such preparation, the 90–95 percent of the activity is lost. Active, very heterogeneous fractions were obtained, by solvent extraction, from « toxohormone ». A globulin fraction from ascitic fluid proved very active; « toxohormone » was prepared also from this fraction but with a loss of 95 percent of the original activity. It is concluded that at least two categories of inhibitors exist, one of proteic nature, and one probably derived from the first, of low molecular weight. For the investigation of such substances, methods less damaging than those employed for « toxohormone » are necessary.

A crystalline substance with marked antimitotic activity on several biological systems (mitoses of ascites S 180, of the megaloblasts of chick embryo, of the tips of wheat radicles) has been isolated from the bulbs of several varieties of Narcissus and named Narciclasine. After reference to the tests that led to its discovery and isolation and to the work of others in the same field, the method of isolation is described together with the physical and chemical properties of the substance (identification, chromatographic behavior, UV, IR and fluorescence). The structural formula, established on the basis of work reported elsewhere, is given.

Tumoral and non-tumoral ascitic fluids, subcutaneously or endoperitoneally injected (2 ml) in normal mice, produce a significant decrease of the liver catalase activity. The only negative results were observed with a liquid from a tubercular pleurisy and another one from cardiocirculatory decompensation. After adsorption of the ascitic liquids on tricalcic phosphate gel, made old or suitably treated, the supernatant exerts, at the same dose, an inhibiting power on liver catalase which is higher than that of the original liquid. Such phenomenon is of difficult interpretation. The inhibiting activity appears to be clearly increased even after prolonged stay at low temperature (–-15 °C).

Two protein fractions, decreasing the liver catalase activity «in vivo», have been prepared from ascitic fluids of tumoral and non tumoral origin, by adsorption on calcium phosphate gel at pH 5, and desorption at pH 8. They are: a globulin fraction, that remains in the ascitic fluid after adsorpitin at pH 5; an albumin fraction that is desorbed at pH 8. The activity of the globulin fraction is due for the most part to low molecular weight substances which are adsorbed to the protein and may be separated from their protein support by dialysis. On the contrary the activity of the albumines has to be ascribed to the protein molecule. Denaturation does not affect the anticatalase activity « in vivo » of albumines, on the contrary it destroys the « in vitro » activity, which is present in the undenatured material.

Seven toxohormone preparations from 4 human tumours, 2 ascites fluids from human cancer, 1 Ehrlich adenocarcinoma were tested for their anticatalase activity «in vitro». Five out of seven were found to inhibit crystalline catalase, depending on the dose employed. In two cases, on the contrary, catalase was increased. All were active «in vivo » on mouse liver catalase.

The dialysable fraction of ascitic fluids, that depresses liver catalase activity, has been studied. This fraction was extracted from ascitic fluids (from cancer patients with peritoneal spread, from cirrhotic patients and from mice bearing' sarcoma 180), after various treatments, by n-butanol at pH 10. It proved to be adsorbed to globulins and to confer them their anticatalasic activity. A chromatographic analysis of the very active material demonstrated its complexity and the plurality of the inhibiting substances. The extreme lability of these factors has, until now, prevented their isolation in a pure state. When degraded, their activity is partially restored by reducing agents. On the basis of several data, it is supposed that they are basic polypeptides with SH and phenolic OH groups, and that they are bound, in the ascitic fluid, to a protein support, probably of glubulinic type.

Like cysteine and some of its derivatives, tyrosine inhibits liver catalase not only « in vitro » but also « in vivo ». Among the analogues of tyrosine tested, dihydroxyphenylalanine and dihydroxyphenethylamine possess « in vitro » the same activity as tyrosine; the activity of p-hydroxyphenylethanolamine is lower; phenylalanine is inactive. The «in vitro» activity seems to be directly correlated with the auto-oxidability of the various compounds. None of the analogues of tyrosine tested was active «in vivo». The depressing activity of cysteine and of tyrosine on liver catalase apparently has no relationship with the similar action of tumors.