Structure and Mechanism of the Caseinolytic Protease ClpP1/2 Heterocomplex from Listeria monocytogenes

Listeria monocytogenes is a devastating bacterial pathogen. Its virulence and intracellular stress tolerance are supported by caseinolytic protease P (ClpP), an enzyme that is conserved among bacteria. L. monocytogenes expresses two ClpP isoforms that are only distantly related by sequence and differ in catalysis, oligomerization, active‐site composition, and N‐terminal interaction sites for associated AAA⁺ chaperones. The crystal structure of the ClpP1/2 heterocomplex from L. monocytogenes was solved, and in combination with biochemical studies, it provides insights into the mode of action. The results demonstrate that structural interlocking of LmClpP1 with LmClpP2 leads to the formation of a tetradecamer, aligns all 14 active sites, and enhances proteolytic activity. Furthermore, the catalytic center was identified as being responsible for the transient stability of ClpPs.     

Zum Mechanismus der Aziridinsynthese aus 2-Azidoalkoholen und Triphenylphosphin

On the Mechanism of the Aziridine Synthesis from 2-Azido-alcohols and Triphenylphosphine The reaction of selected 2-azido-alcohols, their pivalates, and methanesulfonates with triphenylphosphine was investigated. It is shown that the formation of aziridines from 2-azido-alcohols proceeds via 1,3,2λ⁵oxazaphospholidines. Furthermore, the first synthesis of the unsubstituted acenaphtene-1,2-imine is described.     

Silicate und Germanate mit der Struktur des Silicocarnotits

Silicates and Germanates with the Structure of Silicocarnotite A number of lanthanoid-containing compounds Ca₃Ln₂(XO₄)₃ with X = Si, Ge have been prepared, which have the silicocarnotite structure. With the silicates, Ln ranges from Sm to Lu, with the germanates only from Sm to Tb. Ca₃Y₂(SiO₄)₃ crystallizes in this structure type, too. In the case of Ln = La? Nd, mixtures “Ca₃Ln₂(XO₄)₃” are formed containing apatite phases. The germanates Ca₃Ln₂(GeO₄)₃ with Ln = Dy? Lu; Y, Sc and Ca₃Sc₂(SiO₄)₃ have the garnet structure, as already known. In addition, the lead compounds Pb₃La₂(SiO₄)₃, Pb₃Y₂(SiO₄)₃ and Pb₂Y₃(SiO₄)₃O_0,5 have been synthesized. They have an apatite structure where the halogen positions are unoccupied or half-occupied.     

Untersuchung der Struktur und Eigenschaften der Polymeren des 2-Methyl-5-?thinylpyridins

Ohne Zusammenfassung     

Mechanismus der elektronenstossinduzierten H2O-eliminierung aus 2-(hydroxymethyl)-cyclohexanol-(1)

By investigation of ²H-labelled compounds it can be established that the hydrogens of the alcohol-functions participate mainly in the electron impact induced H₂O-elimination from 2-(Hydroxymethyl)-cyclohexanol-(1). The hydrogens of the (C₁)- as well as the (C₇)-positions play only a small part in the fragmentation. By means of an ¹⁸O-labelled diol it can be shown that the oxygen of the primary hydroxyl-function is eliminated preferentially. The stereochemistry of the compounds does not influence the mechanism of the H₂O-elimination.     

Zum Mechanismus der photochemischen Umwandlung von 2-Alkyl-indazolen in 1-Alkyl-benzimidazole. I. Struktur und Reaktivität eines Zwischenproduktes

Mechanistic studies on the photoisomerization of 2-alkyl-indazoles into 1-alkyl-benzimidazoles. I. Structure and reactivity of an intermediate. 2-Alkyl-indazoles ( 1 ) undergo photochemical isomerization to 1-alkyl-benzimidazole via previously unknown intermediates 3 (Scheme 1). In the present paper the structure and reactivity of these intermediates are discussed. Low-temperature irradiation (?60°) of 1 b with 300 nm light gives 3 b in quantitative yield. 3 b is transformed during warm-up to 1 b and 2 b (UV.-evidence). The formations of 1 and 2 show the same temperature dependence but their ratio is found to be temperature-independent. In contrast to the above behaviour, low-temperature irradiation with 250 nm light of 3 b yields 1 b only (no 2 b ). These findings are consistent with the proposed reaction mechanism 2 c in Scheme 2. On the basis of spectroscopic properties and the described reaction pathways, it appears that the most suitable structure for intermediate 3 is a 7,8-diaza-tricyclo[4.3.0.0^7,9]nona-2,4,6(10)-trien ( 9 ). In Scheme 4 the reaction pathway for the iudazole-benzimidazole-rearrangement is summarized.