Bacteria enzyme studies with

The 3-ketothiolase has been purified and investigated from several poly(3HB)-synthesizing bacteria including Azotobacter beijerinckii [10], Ral-stonia eutropha [11], Zoogloea ramigera [12], Rhodococcus ruber [13], and Methylobacterium rhodesianum [14]. In R. eutropha the 3-ketothiolase occurs in two different forms, called A and B, which have different substrate specificities [11,15]. In the thiolytic reaction, enzyme A is only active with C4 and C5 3-ketoacyl-CoA whereas the substrate spectrum of enzyme B is much broader, since it is active with C4 to C10 substrates [11]. Enzyme A seems to be the main biosynthetic enzyme acting in the poly(3HB) synthesis pathway, while enzyme B should rather have a catabolic function in fatty-acid metabolism. However, in vitro studies with reconstituted purified enzyme systems have demonstrated that enzyme B can also contribute to poly(3HB) synthesis [15]. 

Under aerobic conditions, aerobic bacteria has so far been only found in studies capable of reducing azo compounds and produce aromatic amines by specific oxygen-catalyzed enzymes called azo reductases. These aerobic bacteria could grow with mostly simple azo compounds as sole source of carbon and energy and under strict aerobic conditions by using a metabolism that started with reductive cleavage of the azo linkage. 

Nucleoside phosphorylases that catalyse the reversible cleavage of purine nucleosides to the free bases and ribose-1-phosphate are found in most cells, although a phosphorylase that will cleave adenosine has so far been identified only in bacteria. Recent studies have shown that ribo- and 2 -deoxyribofurano-syltransferase activity is associated with phosphorylase activity [19, 23., 222] and that both activities reside in one enzyme, which can be converted from one form to the other by substrate or product binding [20]. Upon crystallization of the enzyme from human erythrocytes a marked decrease in the ribosyl transfer reaction was observed [21b]. 

Currently there is no experimentally determined three-dimensional structural information available for OSCs, although studies with a related enzyme, squa-lene-hopene cyclase (SC EC 5.4.99.7) have proved informative. SCs are involved in the direct cyclisation of squalene to pentacyclic triterpenoids known as hopanoids, which play an integral role in membrane structure in prokaryotes [ 51 ]. A number of SC genes have been cloned from bacteria [52 - 54]. The SC and OSC enzymes have related predicted amino acid sequences, and so should have similar spatial structures [55]. The crystal structure of recombinant SC from the Gram-positive bacterium Alicyclobacillus acidocaldarius has established that the enzyme is dimeric [55]. Each subunit consists of two a-a barrel domains that assemble to form a central hydrophobic cavity [55,56]. 

The predilection of bacteria to associate with surfaces is the primary organizing principle of community structure. ZoBell (1943) presented a conceptual model of this organization surfaces concentrate nutrients bacterial attachment to surfaces maximizes concentration gradients and reduces diffusion distances packing cells on surfaces improves retention of extracellular enzymes. Over the next 40 years, the study of attached microbial communities became an integral part of several fields (see Chapter 12). The importance of periphyton, or aufwuchs, in stream metabolism was established (Hynes, 1970 Geesey et al., 1978 Stevenson et al., 1996). Comparative studies of community organization and activity in relation to substratum produced a taxonomy for attached communities epilithon, epiphyton,... 

One of the second type of inhibitor analogs which cause a time-dependent inactivation of alanine racemase is (l-aminoethyl)phosphonic acid, the phosphonate analog of alanine (Ala-P). Ala-P effectively and specifically inactivates alanine racemases from Grampositive bacteria (Bacillus, Staphylococcus, Streptococcus), and serves as a reversible inhibitor of Gram-negative bacterial (Escherichia, Salmonella) alanine racemase.47 53 The mechanism of inhibition was studied with B. stearothermophihis alanine racemase.47 The d- or L-Ala-P leads to an E-I complex with a Ki value of 1 mM, then is slowly isomerized (A nac<=6-9 min-1) to a stoichiometric enzyme complex (E-I ). The Ed dissociates extremely slowly with the... 

The localization of different PBPs and peptidoglycan hydrolases in several bacterial species has been determined using immunofluorescence and, more recently, using GFP-fusions [106, 107,108,109,110]. From these studies, it appears that in coccoid bacteria cell wall synthesis occurs mainly at the septum, while in rod-shaped bacteria different PBPs are localized to sites of cell division and peripheral cell wall synthesis. Furthermore, the localization of the enzymes seems to be dependent on both interactions with other enzymes and with substrate [98]. These visualization techniques have also helped explain the apparent functional redundancy of the PBPs. For example, in S. pneumoniae, different PBPs are speciflcally localized to sites of... 

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