Ralph K. Barclay

Effects of N-Methylformamide and Related Compounds in Mouse Sarcoma 180.

Summary and Conclusions 1. Formamide and its more potent N-methyl derivative have been described as transient inhibitors of the growth of mouse sarcoma 180. This effect is not a property of formamides in general since other compounds containing the formamide moiety have failed to affect the growth of the tumor. 2. N-methylformamide has been shown to exert its effects when therapy is started either 24 or 96 hours after implantation of the tumor or when the agent is given in a single, large dose. Further, the compound has been found equally effective whether given by the oral or intraperitoneal route. 3. Histologic changes of a non-specific nature have been described in tumors from animals treated with N-methylformamide. 4. In view of the structural resemblance between formamide and urethane, the actions of both agents have been compared. Urethane, like formamide, inhibits the growth of S-180; however, treatment with the former substance causes toxic manifestations not encountered in mice given formamide. 5. Several conceivable mechanisms have been proposed to account for the inhibitory effects of the formamides. Further studies of these suggested modes of action may provide useful information concerning biochemical mechanisms involved in the growth of tumors. 6. In view of the hepatotoxicity of formamide and its N-methyl derivative it is not expected that these agents will prove therapeutically useful.

Studies on plasma membranes from liver cells separation and characterization of lipoprotein subunits of the isolated plasma membranes

1. 1. High-density lipoproteins were separated from plasma membranes solubilized by brief sonication. 2. 2. The three more soluble lipoproteins have increasingly higher hydrated densities along with decreasingly lower lipid-protein ratios and flotation properties (sf) in the analytical ultracentrifuge. 3. 3. A less soluble lipoprotein, the pellicle, floats out mainly at solution density 1.17 g/ml. It appears as quasicrystalline needles which have a lamellar appearance under phase contrast microscopy. 4. 4. The greatest specific activities for the two principal membrane-localized enzymes, 5′-nucleotidase (EC 3.1.3.5) and (Na+-K+)-ATPase (EC 3.6.1.3) are associated with the soluble lipoprotein which has the lowest density, e.g.d < 1.125 g/ml. Different and decreasing amounts of activity are associated with the other soluble lipoproteins as their densities increase. The pellicle, also, has significant specific activity. 5. 5. The three soluble lipoproteins are present in liver plasma membranes from normal young rats in the following proportional quantities: lipoproteins (A) with d < 1.125, 25–30%; (B) with d < 1.17, 55–60%; and (C) with d < 1.21 g/ml, 10–15%. These amounts occur with regularity and are reproducible from experiment to experiment when the rats are young. In older (at least 1 year) and somewhat heavier rats, the majority of the total lipoprotein content is shifted to lipoprotein A. 6. 6. The reproducibility of the quantities as well as the association of the activities for the two enzymes, suggest that the plasma membranes from young rat liver may be composed of units or subunits which are present in a pattern in the structural organization and that they have different biochemical properties.

Determination of acid-soluble thiols and disulfides in transplanted animal tumors

Abstract The concentration of acid-soluble thiols and disulfides was measured in the deproteinized supernatant fractions of homogenates of seven transplanted mouse tumors and two rat tumors. Disulfides were determined after reduction to thiols with sodium borohydride in alkaline medium. Levels of both the reduced and oxidized forms of acid-soluble sulfur-containing peptides were of a similar magnitude. Certain details of the preparation of tissue samples were examined. Homogenization in an acid medium in the presence of high concentrations of sodium ethylenediaminetetraacetate is required to preserve the endogenous thiols from auto-oxidation. Reduction of disulfides with sodium borohydride must precede deproteinization to obtain high degrees of recovery of added oxidized glutathione standards. Reduction with zinc in an acid medium resulted in much lower and irregular recovery. Saturation with ammonium sulfate of tissue samples to be deproteinized did not improve the recovery of added internal standards of glutathione. Deproteinization of tissue samples with perchloric or sulfosalicylic acids produced superior results compared with samples deproteinized with metaphosphoric or trichloroacetic acids.