The site of action of a Vero toxin (VT2 or Shiga‐like toxin II) from enterohemorrhagic Escherichia coli and Shiga toxin from Shigella dysenteriae 1 on eukaryotic ribosomes was studied. Treatment of eukaryotic ribosomes with either toxin caused the release of a fragment of 400 nucleotides from 28S ribosomal RNA when the isolated ribosomal RNA was treated with aniline. Release of this fragment with aniline treatment was accompanied by inhibition of protein synthesis and of elongation‐factor‐1‐dependent aminoacyl‐tRNA binding to ribosomes. Analysis of the nucleotide sequence of the 3′‐terminal fragment of 553 nucleotides of 28S rRNA of rat liver 60s ribosomal subunits suggested that an adenine base at position 4324 (A‐4324) was absent in toxin‐treated 28S rRNA. Further analysis by thin‐layer chromatography demonstrated quantitative release of adenine from rat liver ribosomes on treatment with the toxins. These results indicate that both VT2 and Shiga toxin inactivate 60S ribosomal subunits by cleaving the N‐glycosidic bond at A‐4324 in 28S ribosomal RNA.

Changes in polyamine levels during aging were measured in 3-, 10- and 26-week-old female mice. The level of polyamines in pancreas, brain, and uterus was maintained during these periods. The level of spermidine slightly decreased in intestine, and decreased significantly in thymus, spleen, ovary, liver, stomach, lung, kidney, heart and muscle during these periods. In skin, the level of spermidine was maximal in 10-week-old mice and markedly reduced in 26-week-old mice. The results suggest that maintenance of polyamine levels may play important roles in the function of the pancreas, brain and uterus in 3- to 26-week-old mice. We next looked for polyamine-rich food materials as a dietary source of polyamines. Foods found to be rich in polyamines included wheat germ, rice bran, black rice, Philippine mango, green pepper, Japanese pumpkin, nuts, fermented pickles, pond smelt, turban shell viscera, whelk viscera, salted salmon roe, salted cod roe, beef intestine (boiled) and liver of eel, beef, pork and chicken; and, as previously reported, soybean, fermented soybean (natto), mushrooms, orange and green tea leaf. These results offer useful information when it becomes necessary to ingest polyamines from food.

Summary: The functions of the putative cadaverine transport protein CadB were studied in Escherichia coli. CadB had both cadaverine uptake activity, dependent on proton motive force, and cadaverine excretion activity, acting as a cadaverine‐lysine antiporter. The Km values for uptake and excretion of cadaverine were 20.8 and 303 µM respectively. Both cadaverine uptake and cadaverine‐lysine antiporter activities of CadB were functional in cells. Cell growth of a polyamine‐requiring mutant was stimulated slightly at neutral pH by the cadaverine uptake activity and greatly at acidic pH by the cadaverine‐lysine antiporter activity. At acidic pH, the operon containing cadB and cadA, encoding lysine decarboxylase, was induced in the presence of lysine. This caused neutralization of the extracellular medium and made possible the production of CO₂ and cadaverine and aminopropylcadaverine instead of putrescine and spermidine. The induction of the cadBA operon also generated a proton motive force. When the cadBA operon was not induced, the expression of the speF–potE operon, encoding inducible ornithine decarboxylase and a putrescine‐ornithine antiporter, was increased. The results indicate that the cadBA operon plays important roles in cellular regulation at acidic pH.