Drugs online research references
Appl Microbiol Biotechnol. 1995 Apr;43(1):123-30.
Analysis of penicillin V biosynthesis during fed-batch cultivations with a high-yielding strain of Penicillium chrysogenum.
Jorgensen H, Nielsen J, Villadsen J, Mollgaard H.
Department of Biotechnology, Technical University of Denmark, Lyngby.
Metabolites (both intra- and extracellular) involved in penicillin biosynthesis were measured during fed-batch cultivations with a high-yielding strain of Penicillium chrysogenum. The fed-batch cultivations were carried out on a complex medium containing corn steep liquor. Three distinct phases were observed: (a) a rapid growth phase where free amino acids present in the medium are metabolized, (b) a linear growth phase, and (c) a stationary phase. The specific penicillin production (rp) is initially high and, during the rapid growth phase, it increases slightly. During the linear growth phase rp is approximately constant [4-6 mg penicillin V (g dry weight)-1 h-1 depending on the operating conditions], whereas it decreases during the stationary phase. During the cultivations the tripeptide Aad-Cys-Val (the first metabolite in penicillin biosynthesis) and 8-hydroxypenillic acid (formed by carboxylation of 6-aminopenicillanic acid, 6-APA) were found to accumulate in the medium, whereas the concentrations of isopenicillin N and 6-APA were found to be approximately constant and low. About 3% of the Aad-Cys-Val formed in the first step of the penicillin biosynthetic pathway is lost to the medium and 4% of the isopenicillin N formed in the second step of the pathway is lost as extracellular isopenicillin N, 6-APA or 8-hydroxypenillic acid. Also the cyclic form of alpha-aminoadipic acid, 6-oxo-piperidine-2-carboxylic acid, was found to accumulate in the medium and it was found to be formed in an approximately constant ratio to penicillin V of 6 mol/100 mol.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7766125&dopt=Abstract
Scand J Infect Dis. 1994;26(3):301-5.
Increasing resistance to penicillin in Streptococcus pneumoniae in southern Sweden.
Ekdahl K, Kamme C.
Department of Infectious Diseases, Lund University Hospital, Sweden.
The susceptibility to penicillin of 6 prevalent pneumococcal types isolated from nasopharynx in 1992 was compared with that of corresponding types from 1980-82. The 6 types or groups, 6, 9, 14, 15, 19 and 23, constituted 78% of consecutive isolates. 19/204 isolates in 1992 were intermediately resistant (MIC 0.12-1.0 mg/l) in comparison with 1/194 from 1980-82 (p < 0.001). Resistant strains (MIC > or = 2 mg/l) were not found. Of group 15, no fewer than 10/31 isolates were intermediately resistant, which may support the clonal origin and spread of penicillin-resistant pneumococci. At least 5.0% of nasopharyngeal isolates are now intermediately resistant to penicillin. This figure is substantially higher than the 2% earlier reported in Sweden.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7939430&dopt=Abstract
Biochem J. 1994 Oct 15;303 ( Pt 2):555-8.
Effects of site-specific mutagenesis of tyrosine 105 in a class A beta-lactamase.
Escobar WA, Miller J, Fink AL.
Department of Chemistry and Biochemistry, University of California, Santa Cruz 95064.
Tyr-105 is a conserved residue in the Class A beta-lactamases and is in close proximity to the active-site. Tyr-105 in beta-lactamase from Bacillus licheniformis was converted into Phe by site-directed mutagenesis. This mutation caused no significant effect on the structure of the enzyme and had only small effects on the catalytic properties. In particular, in comparison to the wild-type, kcat. for benzylpenicillin was increased slightly, whereas it was decreased slightly for several other substrates. For each substrate examined, Km increased 3-4-fold in the mutant compared with the wild-type enzyme. Examination of the effect of pH on the catalytic reaction revealed only small perturbations in the pK values for the acidic and basic limbs of the kcat./Km pH profiles due to the mutation. Overall effects of the Y105F substitution on the catalytic efficiency for different penicillin and cephalosporin substrates ranged from 14% to 56% compared with the wild-type activity. We conclude that Tyr-105 is not an essential residue for beta-lactamase catalysis, but does contribute to substrate binding.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7980417&dopt=Abstract
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