Acetyl-coenzyme A carboxylase (Ac-CoA carboxylase; EC 6.4.1.2) catalyzes the rate-limiting reaction in long-chain fatty acid biosynthesis. To investigate the mechanism of genetic control of expression of Ac-CoA carboxylase and the relationship between its structure and function, cDNA clones for Ac-CoA carboxylase were isolated. The complete coding sequence contains 7035 bases; it encodes a polypeptide chain of 2345 amino acids having a Mr of 265,220. The sequences of several CNBr peptides of Ac-CoA carboxylase were localized within the predicted protein sequence as were those peptides that contain the sites for phosphorylation. The deduced protein contains one putative site for biotinylation in the NH2-terminal half. The "conserved" biotinylation site peptide, Met-Lys-Met, is preceded by valine, whereas alanine is found in a similar position in all other known biotincontaining proteins. The primary sequences of Ac-CoA carboxylase and carbamoyl phosphate synthetase exhibit substantial identity.
Acetyl-CoA carboxylase, the rate-limiting enzyme in the biogenesis of long-chain fatty acids, is regulated by phosphorylation and dephosphorylation. The major phosphorylation sites that affect carboxylase activity and the specific protein kinases responsible for phosphorylation of different sites have been identified. A form of acetyl-CoA carboxylase that is independent of citrate for activity occurs in vivo. This active form of carboxylase becomes citrate-dependent upon phosphorylation under conditions of reduced lipogenesis. Therefore, phosphorylation-dephosphorylation of acetyl-CoA carboxylase is the enzyme's primary short-term regulatory mechanism; this control mechanism together with cellular metabolites such as CoA, citrate, and palmitoyl-CoA serves to fine-tune the synthesis of long-chain fatty acids under different physiological conditions.
The surface modification of orthodontic wires with photocatalytic TiO(2) can be used to prevent the development of dental plaque during orthodontic treatment.
A variety of nuruk were collected from various provinces in Korea, and their microflora profiles were analyzed at the species level. A total of 42 nuruk samples were collected and when the viable cell numbers in these nuruk were enumerated, the average cell numbers of bacteria, fungi, yeast, and lactic acid bacteria from all nuruk were 7.21, 7.91, 3.49, and 4.88 log CFU/10 g, respectively. There were no significant differences in viable cell numbers of bacteria or fungi according to regions collected. Bacillus amyloliquefaciens and B. subtilis were the predominant bacterial strains in most samples. A significant portion, 13 out of 42 nuruk, contained foodborne pathogens such as B. cereus or Cronobacter sakazakii. There were various species of lactic acid bacteria such as Enterococcus faecium and Pediococcus pentosaceus in nuruk. It was unexpectedly found that only 13 among the 42 nuruk samples contained Aspergillus oryzae, the representative saccharifying fungi in makgeolli, whereas a fungi Lichtheimia corymbifera was widely distributed in nuruk. It was also found that Pichia jadinii was the predominant yeast strain in most nuruk, but the representative alcohol fermentation strain, Saccharomyces cerevisiae, was isolated from only 18 out of the 42 nuruk. These results suggested that a variety of species of fungi and yeast were distributed in nuruk and involved in the fermentation of makgeolli. In this study, a total of 64 bacterial species, 39 fugal species, and 15 yeast species were identified from nuruk. Among these strains, 37 bacterial species, 20 fungal species, and 8 yeast species were distributed less than 0.1%.
A chitinase gene (chiA) from Pseudomonas sp. YHS-A2 was cloned into Escherichia coli using pUC19. The nucleotide sequence determination revealed a single open reading frame of chiA comprised of 1902 nucleotide base pairs and 633 deduced amino acids with a molecular weight of 67,452 Da. Amino acid sequence alignment showed that ChiA contains two putative chitin-binding domains and a single catalytic domain. Two proline-threonine repeat regions, which are linkers between catalytic and substrate-binding domains in some cellulases and xylanases, were also found. From E. coli, ChiA was purified 12.8-fold relative to the periplasmic fraction. The Michaelis constant and maximum initial velocity for p-nitrophenyl-N,N'-diacetylchitobiose were 1.06 mM and 44.4 micromol/h per mg protein, respectively. The purified ChiA binds not only to colloidal chitin but also to other substrates (avicel, chitosan, and xylan), but the binding affinity of avicel, chitosan, and xylan is around 10 times lower than that of colloidal chitin. The reaction of ChiA with colloidal chitin and chitooligosaccharides (trimer-hexamer) produced an end product of N,N'-diacetylchitobiose, indicating that ChiA is a chitobiosidase.
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