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Summary o 1. Methods for the detection of steroids in paper chromatography have been described and evaluated for 31 compounds. 2. A new method of detection of steroids involving phosphomolybdic acid has been reported. 3. A method using silicotungstic acid has been extended to cover many new compounds.

Silicotungstic acid on silica gel is a very active solid acid catalyst. The influence of a number of variables in the preparation of the catalyst has been studied. A simple method for determining its activity has been developed and used to investigate the effect of different pretreatments given to some silica gels as well as the influence of the percentage of silicotungstic acid and of particle size. It was found that the silica gel with the largest average pore diameter gave the most efficient catalyst. This gel had the smallest specific surface area. The catalytic activity increased substantially as the catalyst particle size was reduced, indicating that only a minor part of the catalyst particles is accessible to the reactants. This conclusion was confirmed by the results of disproportionation experiments performed with cumene. The throughput could be increased about 10 times — the percentage of cumene conversion remaining constant — when the particle size was reduced by a factor of 7. It appeared that 90 per cent of the equilibrium conversion could still be obtained at the extremely high L.H.S.V. of 40 1/hr 1., using a catalyst sieve fraction of 0·3–0·6 mm. The diameter of a silicotungstic acid molecule and the surface area of a mono-molecular layer formed by 1 g of this acid as calculated from crystallographic data were found to be 10 A and 200 m2, respectively.

Phosphotungstic acid and silicotungstic acid, when employed at low concentrations (≤ 0.2 mg/mg protein), were found to markedly inhibit mitochondrial respiration stimulated by either ADP or 2,4-dinitrophenol. At higher concentrations these negative staining agents were found to solubilize significant amounts of mitochondrial protein. The results clearly show that PTA and STA are not biochemically inert and probably have more than a single mitochondrial site of action.

SummaryAn inhibitor (STAS) prepared from the supernatant of JLS-V5 cells blocked the replication of MLV in vitro when added to MEF cultures as late as 48 hr after but not prior to infection with MLV. Potent antiviral activity against MLV was also observed with inhibitor prepared from JLS—V9 tissue culture supernatant fluid, fetal calf serum (FCS), normal Balb/c mouse plasma, MEM + 10% FCS, saline, or silicotungstic acid (STA). Inhibitor prepared from JLS-V5 supernatant fluid, but substituting ZnSO4 PCA, TCA, ethanol, or ammonium sulfate precipitants instead of STA, showed little or no activity against MLV in vitro. No viracidal activity was obtained when MLV was exposed directly to JLS-V5 STAS. These studies suggest that the active ingredient in JLS-V5 STAS may be silicotungstic acid.

A negative stain should produce no structural change in the specimen. Our results indicate that this is not the case with at least two negative stains. There is a spectrum of changes which depends on the stain used. The negative stain also causes functional alterations which involve three basic functional characteristics of the mitochondria: 1) oxidative phosphorylation, 2) electron transport and 3) ion permeability. Rat kidney mitochondria were resuspended in the negative stain for 15 minutes (except for kinetic studies). For electron microscopy they were: 1) directly applied to grids; 2) fixed with glutaraldehyde and OSO4 and embedded in Epon; and 3) prepared by freeze fracturing. Mitochondria stained with ammonium molybdate (AM) revealed two types of profiles. They had either a dense inner compartment without penetration of negative stain displaying the commonly observed image (Fig. 3 and 4). With penetration the inner membrane was studded with spheres, but the spheres were not on discernible stalks (Fig. #5).