John F. Thomson

Liposome-Encapsulated Actinomycin D: Potential in Cancer Chemotherapy

Summary Actinomycin D, when encapsulated within liposomes, is less toxic to mice than the nonencapsulated form. A single dose (0.75 mg/kg) or multiple doses (1 × 0.50, 4 × 0.25 mg/kg) significantly increased the mean survival time of mice inoculated with Ehrlich ascites tumor cells. Liposomes containing actinomycin D were found in tumor cells and cell degeneration and death were subsequently observed.

Further studies on cytoplasmic particulates isolated by gradient centrifugation.

Abstract 1. 1. The use of gradient centrifugation to study the distribution of cytoplasmic components of rat and mouse liver has been further explored. The method for calculation of particle sizes has been revised by considering the effects of the osmotic-pressure gradient. 2. 2. Data obtained on tissue which was not mashed prior to homogenization are presented for comparison with earlier results. The use of the masher has a deleterious effect on mitochondria, but apparently not on other subcellular particles. 3. 3. Mitochondria isolated by gradient centrifugation are capable of efficient oxidative phosphorylation, regardless of whether or not the tissue was mashed. The total yield of active material is less from mashed tissue. 4. 4. Among the enzymes studied in both rat and mouse liver, catalase was found by our technique to differ markedly in the two species, being associated with microsomes in rats and with uricase-containing particles in mice. The former is recognized as an artifact of redistribution. 5. 5. The question of association of enzymes reputedly found only in mitochondria with particles of microsomal size is discussed.

Enzymatic activity of cytoplasmic particulates of rat liver isolated by gradient centrifugation.

Abstract The relative distribution of several enzymes in respect to size of cytoplasmic particles has been established by centrifugation of rat liver homogenates through concentration-gradient solutions of sucrose. The particle sizes associated with maximum total activity are not necessarily the same as those associated with maximum enzyme concentration.

Spectrophotometric Assay of Catalase with Perborate as Substrate

Summary A spectrophotometric assay for catalase has been developed in which sodium perborate, rather than hydrogen peroxide, is used as the substrate. The method is convenient, rapid, and readily adapted to the measurement of catalase in subcellular fractions.

Dose-response modeling of life shortening in a retrospective analysis of the combined data from the JANUS program at Argonne National Laboratory.

Life shortening was investigated in both sexes of the B6CF1 (C57BL/6 x BALB/c) mouse exposed to fission neutrons and 60Co gamma rays. Three basic exposure patterns for both neutrons and gamma rays were compared: single exposures, 24 equal once-weekly exposures, and 60 equal once-weekly exposures. Ten different dose-response models were fitted to the data for animals exposed to neutrons. The response variable used for all dose-response modeling was mean after-survival. A simple linear model adequately described the response to neutrons for females and males at doses less than or equal to 80 cGy. At higher neutron dose levels a linear-quadratic equation was required to describe the life-shortening response. An effect of exposure pattern was observed prior to the detection of curvature in the dose response for neutrons and emerged as a potentially significant factor at neutron doses in the range of 40-60 cGy. Augmentation of neutron injury with dose protraction was observed in both sexes and began at doses as low as 60 cGy. The life-shortening response for all animals exposed to gamma rays (22-1918 cGy) was linear and inversely dependent upon the protraction period (1 day, 24 weeks, 60 weeks). Depending on the exposure pattern used for the gamma-ray baseline, relative biological effectiveness (RBE) values ranged from 6 to 43. Augmentation, because it occurred only at higher levels of neutron exposure, had no influence on the estimation of RBEm.

Effect of total body x-irradiation on the tryptophan peroxidase activity of rat liver.

Summary Total-body x-irradiation produces within a few hours a dose-dependent increase in the tryptophan peroxidase-oxidase system of rat liver. The increase does not occur in adrenalectomized rats, and hence cannot be construed as a direct effect of x-irradiation.

Isotope and solvent effects of deuterium on aconitase.

Abstract The activity of aconitase has been compared in H 2 O and in 99% D 2 O, with deuteriocitrate and deuterioisocitrate as well as the protiated substrates, citrate, isocitrate, and aconitate. The rates of all six interconversions were markedly inhibited by D 2 O; the conversion of aconitate to citrate was affected much more than the conversion of aconitate to isocitrate. The values obtained for Michaelis constants and maximum velocities satisfactorily predict equilibrium conditions in H 2 O and D 2 O. Negligible isotope effects were observed with deuteriocitrate or deuterioisocitrate; this observation is consistent with the hypothesis that the first (and rate-limiting) step in the dehydration of these compounds is the rupture of the CO rather than the CH bond.

Studies on rat liver ribonucleases: II. Zonal centrifugation of acid ribonuclease; implications for the heterogeneity of lysosomes

Abstract Results obtained by zonal gradient centrifugations demonstrated that rat liver lysosomes are heterogeneous in terms of their enzyme contents. It is suggested that acid phosphatase and cathepsin C on one hand, and acid ribonuclease and cathepsin D on the other, belong to two different classes of “lysosomes”.

Some metabolic characteristics of brown fat, with particular reference to the mitochondria☆

Abstract 1. 1. Mitochondria from the axillary brown adipose tissue of euthermic hibernating and newly-aroused ground squirrels (Citellus tridecemlineatus) have been prepared and assayed for a number of enzyme systems. 2. 2. The sedimentation behavior of brown fat mitochondria is considerably different from that of liver mitochondria, although the equilibrium density, measured by isopycnic centrifugation, is the same for both. 3. 3. Although the respiratory capacity of brown fat mitochondria is very high, they lack the capacity (a) to esterify inorganic phosphate, (b) to accumulate calcium phosphate or (c) to undergo reversibility of swelling induced by thyroxin or glutathione. 4. 4. The intracellular distribution of various enzymes in brown fat is qualitatively similar to that seen in other tissues; although the mitochondria-linked enzymes are present to a significantly greater extent in brown fat than in liver, the concentrations of non-mitochondrial enzymes such as acid phosphatase, catalase and glucose-6-phosphatase are much lower. 5. 5. In general, enzymatic activities of brown fat were somewhat higher in the aroused, and lower in the hibernating ground squirrels, in comparison with the euthermic animals.

The intracellular distribution of a bound acid phosphatase of rat liver as studied by gradient centrifugation

Abstract Gradient centrifugation has been employed to study the intracellular distribution of an acid phosphatase of rat liver which presumably exists in a bound form but can be activated by various means. This distribution pattern resembles that of no other enzyme studied by this method with the possible exception of uricase.