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.

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.

Some observations on the acute histopathologic effects of cycloheximide in vivo

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