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Abrin and ricin: structure and mechanism of action of two toxic lectins
Toxkon, 1977. Vol. 13, pp . 177-176. >
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REVIEWS Jexa, T. W. and Fx.~xxEr.-CornenT, H. (Department of Molecular Biology and the Virus Laboratory, University of California, Berkeley, California) . Activation of Crotoxin B by Volvatoxin A2 . Biochem. biopbys. Res . Commun . 70, 1324 (197 . CltozoxnJ B is a basic component of the venom of the Brazilian rattlesnake Crotalus durissus terriflcus which is weakly neumtoxic in the absence of its complexing protein Crotoxin A. The neurotoxic potency of Crotoxin B is markedly enhanced by complex formation with a protein from the mushroom Volvuriella volvaces designated as Volvatoxin A2 . The stable complex with Volvatoxin A2 leading to synergistic increase in the neurotoxicity of Crotoxin B appears to be a ono-to-one adduct, although highest biological activity may be favored by the presence of an additional molecule of Crotoxin B. The complex formation involves more specific binding properties of itscomponents than just generalized acid-base interaction. S.L.F.
Olst~s, S. (Norsk Hydro's Institute for Cancer Research, Montebello, Oslo 3) .Abrisandricin: struoture and mechanism of action of two toxic ledins . Bull. Inst. Pasteur, Ptrris 74, 85-99 (197 . Aelux and ricin, the toxic proteins from Ricibus comrnunts beans and Abriss precbtorius seeds were purified by means of affinity chromatography on Sepharose, separating the agglutinins, which have about twice the molecular weight of the toxins, by ion exchange chromatography . Tho toxins were glycoproteins with molecular weights of 65,000. Both consist of two polypeptide chains, one neutral, the other acidic, connected by a single disulphide bond . The B chain of abrin contains carbohydrate . In rids both chains are glycoproteins . The polypeptide chains of the toxins and the toxins were immunologically unrelated. The toxins were very toxic: 13 ng kill mice and picograms per ml kill cell cultures . They did not inhibit growth of bacteria . Only the intact toxins were effective, inhibiting first proteinthen DNA and lastly RNA synthesis. Lactose was a potent inhibitor for the binding of the toxins. With lactose good protection was apparent with rids more than with abrin. There was a linear relationship between the amount of lactose and the quantity of toxin tbecessary for 50 ~ protein synthesis inhihition but the amount of toxin actually bound to the cells at 50 ~protein synthesisinhibition was the same with variation of the toxin amount 300 times. The toxic effect was determined by the number of toxin molecules bound to the cell surface. The A chain inhibits protein synthesis by acting on the 60S subunits of ribosomes of the eukaryotic cell . Ribosomes from toxin treated He-La cells reduced activity in the cell free protein synthetizing system by a direct mechanism. The A chain penetrates through the membrane into the cytoplasm. Thus, it might be that, like diphtheria and cholera toxins, the B chains of rids and abrin bind to the cell surfaceand facilitate the uptake of the A chain through the membrane H.R.
Bxunfl llc, J. (Department of Neurology, Stritch School of Medicine, Loyola University Medical Center, Maywood, Ill.) . Myasthenia gravis associated with wasp sting. J. Am . med. Ass. 235, 2120 (197 . Ix ~ 52-year-old man, without a past history of Hymenoptera stings, simultaneous stings by 3 paper wasps (Polistes) on the left index finger gave rise to a clinical picture of an ocular form of myasthenia gravis with ptosis . The author is of the opinion that this may be due to a direct toxic effect of some components of the wasp venom upon actylcholine synthesis, release or degradation, rather than an immediate hypersensitive reaction . It may be, as pointed out by other authors, the patient had a subclinical case of myasthenia gravis which was triggered by the wasp venom. Z .M . 173
on Preis. Printed in Cheat Britain.
REVIEWS Jexa, T. W. and Fx.~xxEr.-CornenT, H. (Department of Molecular Biology and the Virus Laboratory, University of California, Berkeley, California) . Activation of Crotoxin B by Volvatoxin A2 . Biochem. biopbys. Res . Commun . 70, 1324 (197 . CltozoxnJ B is a basic component of the venom of the Brazilian rattlesnake Crotalus durissus terriflcus which is weakly neumtoxic in the absence of its complexing protein Crotoxin A. The neurotoxic potency of Crotoxin B is markedly enhanced by complex formation with a protein from the mushroom Volvuriella volvaces designated as Volvatoxin A2 . The stable complex with Volvatoxin A2 leading to synergistic increase in the neurotoxicity of Crotoxin B appears to be a ono-to-one adduct, although highest biological activity may be favored by the presence of an additional molecule of Crotoxin B. The complex formation involves more specific binding properties of itscomponents than just generalized acid-base interaction. S.L.F.
Olst~s, S. (Norsk Hydro's Institute for Cancer Research, Montebello, Oslo 3) .Abrisandricin: struoture and mechanism of action of two toxic ledins . Bull. Inst. Pasteur, Ptrris 74, 85-99 (197 . Aelux and ricin, the toxic proteins from Ricibus comrnunts beans and Abriss precbtorius seeds were purified by means of affinity chromatography on Sepharose, separating the agglutinins, which have about twice the molecular weight of the toxins, by ion exchange chromatography . Tho toxins were glycoproteins with molecular weights of 65,000. Both consist of two polypeptide chains, one neutral, the other acidic, connected by a single disulphide bond . The B chain of abrin contains carbohydrate . In rids both chains are glycoproteins . The polypeptide chains of the toxins and the toxins were immunologically unrelated. The toxins were very toxic: 13 ng kill mice and picograms per ml kill cell cultures . They did not inhibit growth of bacteria . Only the intact toxins were effective, inhibiting first proteinthen DNA and lastly RNA synthesis. Lactose was a potent inhibitor for the binding of the toxins. With lactose good protection was apparent with rids more than with abrin. There was a linear relationship between the amount of lactose and the quantity of toxin tbecessary for 50 ~ protein synthesis inhihition but the amount of toxin actually bound to the cells at 50 ~protein synthesisinhibition was the same with variation of the toxin amount 300 times. The toxic effect was determined by the number of toxin molecules bound to the cell surface. The A chain inhibits protein synthesis by acting on the 60S subunits of ribosomes of the eukaryotic cell . Ribosomes from toxin treated He-La cells reduced activity in the cell free protein synthetizing system by a direct mechanism. The A chain penetrates through the membrane into the cytoplasm. Thus, it might be that, like diphtheria and cholera toxins, the B chains of rids and abrin bind to the cell surfaceand facilitate the uptake of the A chain through the membrane H.R.
Bxunfl llc, J. (Department of Neurology, Stritch School of Medicine, Loyola University Medical Center, Maywood, Ill.) . Myasthenia gravis associated with wasp sting. J. Am . med. Ass. 235, 2120 (197 . Ix ~ 52-year-old man, without a past history of Hymenoptera stings, simultaneous stings by 3 paper wasps (Polistes) on the left index finger gave rise to a clinical picture of an ocular form of myasthenia gravis with ptosis . The author is of the opinion that this may be due to a direct toxic effect of some components of the wasp venom upon actylcholine synthesis, release or degradation, rather than an immediate hypersensitive reaction . It may be, as pointed out by other authors, the patient had a subclinical case of myasthenia gravis which was triggered by the wasp venom. Z .M . 173