RESUMEN
[formula: see text] In this Letter we demonstrate the viability of a highly stereoselective tandem Mannich cyclization-grammine fragmentation/addition cascade, critical for assembly of the A and F rings of penitrem D. We also explored simultaneous execution of this tactic with concurrent construction of ring I. Reinvestigation of a model system provided an explanation for the unanticipated stereochemical outcome at C(28).
Asunto(s)
Alcaloides/química , Indoles/química , Micotoxinas/química , Temblor/inducido químicamente , Alcaloides/efectos adversos , Estructura Molecular , EstereoisomerismoRESUMEN
We have developed a substrate to assay for an isopeptidase, an enzyme capable of cleaving the Nepsilon-(gamma-glutamic) lysine bond which crosslinks polypeptide chains. This substrate consists of modified lysine (N-alpha-[3H]acetyl-l-lysine-N-methylamide or ALMA), linked by its epsilon-amino group to a gamma-carboxyl amide group of casein with guinea pig liver transglutaminase or Factor XIIIa. We used this substrate to demonstrate the release of [3H]ALMA from [3H]ALMA-casein in a culture medium of Bacillus cereus and in brain homogenates of 12- to 14-day-old embryonic chicks. The prokaryotic and the eukaryotic enzymes resemble each other in that both are activated by Ca2+ or Mg2+ and by alkaline phosphatase and both are inhibited by ATP. The [3H]ALMA-casein is a sensitive substrate able to measure reliably specific activities as low as 10(-8) micromol of [3H]ALMA/min/microg protein. The special advantage of this substrate is that the initial rate of ALMA-casein cleavage is not affected significantly by the levels of protease contaminants we have encountered. We were able to rule out alternative mechanisms such as gamma-glutamyl transpeptidase, gamma-glutamyl cyclotransferase, and the reversal of transglutaminase. We conclude that an isopeptidase mechanism most plausibly accounts for the ALMA release.
Asunto(s)
Liasas de Carbono-Nitrógeno , Liasas/metabolismo , Lisina/análogos & derivados , Animales , Calcio/farmacología , Caseínas/metabolismo , Embrión de Pollo , Cromatografía en Capa Delgada , Cobayas , Hígado/enzimología , Magnesio/metabolismo , Transglutaminasas/metabolismoRESUMEN
We report a case of salmonella gastroenteritis with recurrent fever and sepsis, slight transient lumbar pain and positive 67Ga-citrate scintigraphy. The 67Ga scan made a major contribution to the positive diagnosis of a subclinical spondylodiscit and to the correct treatment leading to the disappearance of the infectious foci.