University of Freiburg

About: University of Freiburg is a education organization based out in Freiburg, Baden-Württemberg, Germany. It is known for research contribution in the topics: Population & Transplantation. The organization has 41992 authors who have published 77296 publications receiving 2896269 citations. The organization is also known as: alberto-ludoviciana & Albert-Ludwigs-Universität Freiburg.

Anaerobic metabolism of aromatic compounds via the benzoyl‐CoA pathway

Abstract: Aromatic compounds are important growth substrates for microorganisms They form a large group of diverse compounds including lignin monomers, amino acids, quinones, and flavonoids Aerobic aromatic metabolism is characterized by the extensive use of molecular oxygen which is essential for the hydroxylation and cleavage of aromatic ring structures The anaerobic metabolism of low molecular mass soluble aromatic compounds requires, of necessity, a quite different strategy In most known cases, aromaticity is broken by reduction and the ring is subsequently opened hydrolytically A small number of different central aromatic intermediates can be reduced, the most common of which is benzoyl-CoA, a compound that is formed as a central intermediate in the degradation of a large number of aromatic growth substrates This review concentrates on the anaerobic aromatic metabolism via the benzoyl-CoA pathway The peripheral pathways that transform growth substrates to benzoyl-CoA include various types of novel reactions, for example carboxylation of phenolic compounds, reductive elimination of ring substituents like hydroxyl or amino groups, oxidation of methyl substituents, O-demethylation reactions and shortening of aliphatic side chains The central benzoyl-CoA pathway differs in several aspects in the denitrifying, phototrophic and fermenting bacteria studied In denitrifying and phototrophic bacteria it starts with the two-electron reduction of benzoyl-CoA to a cyclic dienoyl-CoA driven by the hydrolysis of two molecules of ATP to ADP+Pi This ring reduction is catalyzed by benzoyl-CoA reductase and requires a low-potential ferredoxin as an electron donor In Rhodopseudomonas palustris the cyclic diene is further reduced to cyclohex-1-ene-1-carboxyl-CoA In the denitrifying species Thauera aromatica, the cyclic diene is hydrated to give 6-hydroxycyclohex-1-ene-1-carboxyl-CoA Subsequent β-oxidation results in the formation of a cyclic β-oxo compound, followed by hydrolytic carbon ring opening yielding 3-hydroxypimelyl-CoA in the case of T aromatica and pimelyl-CoA in the case of R palustris These intermediates are further β-oxidized via glutaryl-CoA; final products are 3 acetyl-CoA and 1 CO2 In fermenting bacteria benzoyl-CoA may possibly be reduced to the level of cyclohex-1-ene-1-carboxyl-CoA in an ATP-independent reaction The genes coding for the enzymes of the central benzoyl-CoA pathway have been cloned and sequenced from R palustris, T aromatica, and Azoarcus evansii Sequence analyses of the genes support the concept that phototrophic and denitrifying bacteria use two slightly different pathways to metabolize benzoyl-CoA The gene sequences have in some cases been very helpful for the identification of possible catalytic mechanisms that were not obvious from initial characterizations of purified enzymes

Mitochondrial Hsp70/MIM44 complex facilitates protein import

Abstract: Protein translocation into mitochondria requires the mitochondria! protein Hsp70. This molecular chaperone of the mitochondrial matrix is recruited to the protein import machinery by MIM44, a component associated with the inner membrane of the mitochondria. Formation of the mt-Hsp70/MIM44 complex is regulated by ATP. MIM44 and mt-Hsp70 interact in a sequential manner with incoming segments of unfolded preproteins and thereby facilitate stepwise vectorial translocation of proteins across the mitochondrial membranes. The complex appears to act as a molecular ratchet which is energetically driven by the hydrolysis of ATP.