Dissociation of effects on protein synthesis and ribosomes from membrane changes induced by carbon tetrachloride

Pretreatment of rats with cycloheximide protects the liver against ribosome changes but not against alterations in the endoplasmic reticulum membrane induced by the administration of CCl(4), as observed both biochemically and ultrastructurally. Another inhibitor of protein synthesis, tenuazonic acid, has effects similar to cycloheximide. Neither compound has any apparent effect when given after the administration of CCl(4) at a time at which a major shift in ribosome distribution from polysomes to ribosome monomers or subunits has already occurred. Thus, it appears that the ribosomes are not susceptible to damage by CCl(4), or more probably an active metabolic derivative of CCl(4), when they are organized as polysomes but only when they are present as monomers or subunits. Also, unlike the situation with ethionine or puromycin, the damage to the protein synthetic system of the ribosomes induced in the liver by CCl(4) appears to be irreversible. In contrast to cycloheximide or tenuazonic acid, N,N'-diphenyl-p-phenylenediamine (DPPD) protects the liver against CCl(4)-induced changes in both ribosomes and endoplasmic reticulum. These observations suggest that the changes in the ribosome-protein synthetic system induced in the liver by treatment with CCl(4) are not the direct result of damage to the membranes of the endoplasmic reticulum but are either an indirect effect of such damage or are unrelated to it. These possibilities are discussed in terms of three proposed working hypotheses.

Studies on acute methionine toxicity. I. Nucleolar disaggregation in guinea pig hepatic cells with methionine or ethionine and its reversal with adenine

The effects of methionine and ethionine on the fine structure of hepatic cell nucleoli of guinea pigs and rats were investigated. A single intraperitoneal injection of methionine into guinea pigs results in the disruption of nucleolonema as early as 2 hours after the injection. By 4 hours, nucleoli show complete fragmentation consisting of many small fragments and small remnants of nucleoli. Large aggregates of interchromatinic granules and condensation of chromatin appear in the nucleoplasm. These changes are remarkably similar to the lesions induced by ethionine in the liver of the rat or the guinea pig. The methionine-induced nuclear and nucleolar lesions persist up to 10 hours after the injection. The administration of adenine 4 hours after the methionine injection reverses the nucleolar lesions by 8 hours. The appearance of incompletely reconstructed nucleoli with twisted ropelike structures suggests a pattern of recovery very similar to the adenine-induced nucleolar reformation in ethionine-treated rats. Injecting methionine into rats induced no nucleolar abnormalities. It is suggested that the mechanism of nucleolar fragmentation induced by methionine or ethionine is related to the accumulation of S-adenosyl compounds with concomitant ATP deficiency in the liver.

Evidence for ethylation of rat liver deoxyribonucleic acid after administration of ethionine

1. Administration of a large dose (500mg/kg body wt.) of (3)H-labelled l-ethionine to rats resulted in the incorporation of a small amount of radioactivity into the liver DNA. Considerable evidence that this radioactivity was not due to contamination of the isolated DNA with labelled protein, RNA, S-adenosyl-l-ethionine or l-ethionine was obtained. 2. After acidic hydrolysis of the DNA isolated from the livers of rats treated with labelled l-ethionine, virtually all of the radioactivity present in the DNA was found in a fraction with similar chromatographic properties to 7-ethylguanine. 3. Treatment of rats with comparable doses of l-methionine did not lead to the formation of 7-methylguanine in the liver DNA. 4. These results are discussed in relation to the induction of liver tumours by ethionine.

Dynamics of injury and repair in hepatic cells. II. Association of membranes with lipid during recovery from ethionine-induced fatty liver

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Partial characterization and cellular localization of two deoxyribonucleases in the small intestine of the rat

We have partially characterized and localized two previously reported deoxyribonucleases from the rat small intestine. After separation of the crypt cells and muscle (the deep layer) from the villus cells (the superficial layer), the latter was found to contain a deoxyribonuclease I with a pH optimum around 6, and a molecular weight of 32 000 – 35 000. It was activated by Co2+, Mg2+, and Mn2+. Ligation of the pancreatic duct reduced the activity in intestinal extracts to about one-third of control levels. A deoxyribonuclease II with a pH optimum of 5.3–5.4 was found associated with the continuously dividing intestinal crypt cells. It was inhibited by Mg2+ and activated by EDTA. Ligation of the pancreatic duct was without effect on this enzyme. The deoxyribonuclease I is probably largely extracellular and serves a digestive function while the deoxyribonuclease II probably is related to intracellular DNA metabolism.