摘要:

AbstractNew enzymatic reactions in supercritical fluid carbon dioxide catalyzed by lipases (PPL, Lipase MY, Candida cylindracea Lipase), and Proteases (subtilisin Carlsberg, subtilisin 8397, immobilized papain) with high efficiency and yields in a simple high pressure reactor using readily available dry‐ice have been develope

ISSN:0009-4536    

DOI:10.1002/jccs.199900091

出版商:WILEY‐VCH Verlag    

年代:1999

数据来源: WILEY

摘要:

AbstractWe present a theory of photocurrent spectra for a light‐emitting diode fabricated by a π‐conjugated polymer system. The tunneling through a barrier induced by the DC field dominates the dissociation of excitor states (i.e., photoionization of vibronic states) below the threshold. The spectra thus obtained explain most of the experimental results and also allows us to more easily position the S2state and other higher states in the conjugated pol

ISSN:0009-4536    

DOI:10.1002/jccs.199900092

出版商:WILEY‐VCH Verlag    

年代:1999

数据来源: WILEY

摘要:

AbstractProtein glycosylation is an important post‐translational event; however, the role carbohydrates play in glycoprotein structure and function is poorly understood, mainly due to the difficulty associated with the synthesis of this class of molecules. This review describes the types and functions of glycopeptides found in nature and the synthesis of biologically active glycopeptides, including vaccines, antibiotics, ligands of receptors involved in signaling, and various structural motifs found in glycoproteins. The synthetic strategies described in this review cover both chemical and enzymatic methods. In addition, structural studies of synthetic glycopeptides and their mimetics, and chemoenzymatic synthesis of complex glycoproteins with well‐defined carbohydrate structure for the study of the effect of glycosylation on protein structure and function are also discus

ISSN:0009-4536    

DOI:10.1002/jccs.199900093

出版商:WILEY‐VCH Verlag    

年代:1999

数据来源: WILEY

摘要:

AbstractThe effect of lovastatin, an HMG‐CoA reductase inhibitor, on the biosynthesis of trichothecin, ergosterol, and fatty acids in the fungusTrichothecium roseumwas investigated. Treatment of lovastatin (50 μM) to a 5‐day‐old culture ofT. roseumreduced the incorporation of [2‐14C]acetate into trichothecin by 79%, whereas the conversion of [5‐3H]mevalonate into this sesquiterpenoid mycotoxin was reduced by only 28%. In a parallel experiment, the incorporation of [2‐14C]acetate and [5‐3H]mevalonate into ergosterol were decreased by 78% and 17%, respectively. Meanwhile, the conversion of labeled acetate into fatty acids was not significantly affected. These results indicate that HMG‐CoA reductase is a major, but not strict, regulatory site in mevalonic acid pathway leading to the formation of trichothecin and ergosterol. No priority was found in utilization of a single, residual mevalonic acid pool in response to lovastatin inhibition for the biosynthesis of trichothecin and ergosterol. Inhibition of mevalonic acid formation does not significantly divert acetyl CoA into fatt

ISSN:0009-4536    

DOI:10.1002/jccs.199900094

出版商:WILEY‐VCH Verlag    

年代:1999

数据来源: WILEY

摘要:

AbstractTriple stranded DNA helix (triplex) formation is limited by pH and the sequence of oligodeoxyribonucleotide. In this study, the 8‐oxo‐2′‐deoxyadenosine (8‐oxoA) can replace 2′‐deoxycytidine for forming a base triad with a base pair guanine and cytosine. The target for the triplex formation is a motif of a promotor (5′‐d‐TTGGGGGGGAA, −3 – −12 of PKCαm‐RNA) of mouse protein kinase Cα. The probes contain 20 bases with a common sequence 5′‐d‐XXXXXXTTCCCCCCAA. The XXXXXX portion may contain either 5‐methyl‐2′‐deoxycytidines, six 8‐oxoA's or both. Only the probe with a motif of six 8‐oxoA's can for triplex with the target in the presence of magnesium ion and spermine at neutral pH. Therefore, 8‐oxoA is useful for

ISSN:0009-4536    

DOI:10.1002/jccs.199900095

出版商:WILEY‐VCH Verlag    

年代:1999

数据来源: WILEY

摘要:

AbstractExchangeable proton information is of critical importance in the NMR structural studies of DNA/RNA oligomers and/or their complexes with protein. However, no systematic NMR assignment strategy about these protons has been reported until now, although similar studies about non‐exchangeable proton assignment have been well established in the past decade. We now report detailed NMR studies of a DNA duplex (d20‐mer) containing the recognition site (5′‐ATGAC‐3′) of GCN4 basic zinc finger protein. All exchangeable and non‐exchangeable protons except H5′/H5″ protons could be assigned from a single H2O/NOESY spectrum at 25°C. The assignment strategy reported in this paper shall be useful to NMR studies of unusual DNA/RNA structures and their complexes with

ISSN:0009-4536    

DOI:10.1002/jccs.199900096

出版商:WILEY‐VCH Verlag    

年代:1999

数据来源: WILEY

摘要:

AbstractA cephalexin‐synthesizing enzyme which catalyzes the synthesis of cephalexin from two substrates, 7‐amino‐3‐deacetoxy cephalosporanic acid (7‐ADCA) and D‐phenylglycine methyl ester (D‐MEPG) was isolated, purified and characterized fromG. oxydansCCRC 10383 by ammonium sulfate precipitation, CM‐Fractogel and Sephadex G‐200 chromatography. The molecular weight of the enzyme was estimated to be 270 kd by gel filtration. From the analysis of SDS‐PAGE, the enzyme is a tetramer and consists of two 53 kd subunits and two 73 kd subunits. The isoelectric point of the enzyme was estimated to be 7.5. The optimal pH and temperature for the synthetic reaction of cephalexin were 5–7 and 30–50°C, respectively, with a maxium reaction rate at pH 6 or 50°C. Metal ions are not essential for the enzymatic activity because EDTA (ethylenediaminetetraacetic acid) exerts no influence upon the enzyme activity. The growth medium containing 0.25% DL‐phenylglycine (DL‐PG) or 0.25% D‐phenylglycine (D‐PG) as inducers could obtain 1.4 times higher enzyme activity than the growth medium without inducers. The values of Km, Kcat, Vmaxand bimolecular constant Kcat/Kmwere 19 mM, 1.2 × 104s−1, 30 unit/mg of protein and 6.2 × 105M−1s−1, respectively. The Kmvalues for D‐MEPG and 7‐ADCA were determined as 13.9 mM and 3.08 mM, respectively. The conversion of cephalexin was found to be 60% when the synthesis was carried out in the 0.1 M phosphate buffer solution (pH 6.2) containi

ISSN:0009-4536    

DOI:10.1002/jccs.199900097

出版商:WILEY‐VCH Verlag    

年代:1999

数据来源: WILEY

摘要:

AbstractProtein tyrosine phosphatases (PTPases) are an important class of enzymes involved in the regulation of many cellular events. Here we describe the design and synthesis of an activity probe 2 targeting these PTPases. This mechanism‐based activity probe adopts a cassette‐like design; a phosphate group serves as the recognition head and a fluorescent diethylaminocoumarin derivative acts as the reporter group. Compound 3 was phosphorylated with diallyl phosphorochloridate and then fluorinated with DAST to give versatile intermediate 5. The Boc protective group of compound 5 was removed by TEA to make available the amino group where a diethylaminocoumarin chromophore was later attached. Final deprotection of the allyl group from the phosphate head gives our complete activity probe 2. It will be used in the labeling study of PTPases from various sour

ISSN:0009-4536    

DOI:10.1002/jccs.199900098

出版商:WILEY‐VCH Verlag    

年代:1999

数据来源: WILEY

摘要:

AbstractWilson disease is an autosomal recessive disorder of copper metabolism, and the defective gene codes for a P‐type Cu2+‐ATPase. Sequence comparison revealed that the Cu2+‐ATPases were very distinct from the Ca2+‐, Na+‐ H+‐, and K+‐ATPases, which however, shared significant similarity to each other. The major difference may be due to the difference in metal ligand preference. Some novel conserved motifs in the Wilson disease protein were also identified, including a putative Walker A motif (GCGIGCKV, residues 1099–1106), and a Walker B motif (GDGVND, residues 1266–1271) for the cofactor ATP binding and hydrolysis, a unique KAPIQ motif (residues 910–914) in the transduction domain, and some motifs in the transmembrane segments probably for the substrate specificity. Combining with the previous genetic and biochemical data, some conserved residues could be assigned for possible functions. This information should provide a guide for designing future studies of structure‐function relationships in the Wilson disease gene. Sequence analysis is also useful in distinguishing whether the mutant residues are missense or polymorphism, such as T977M was identified as a missense mutation because only small amino acid residues ap

ISSN:0009-4536    

DOI:10.1002/jccs.199900099

出版商:WILEY‐VCH Verlag    

年代:1999

数据来源: WILEY

摘要:

AbstractHypusine, an unusual amino acid, is derived from the hydrolysis of eukaryotic initiation factor 5 A (eIF‐5A), the only cellular protein known to contain hypusine residue. Hypusine residue is formed through a spermidine‐dependent posttranslational modification of eIF‐5A at a specific lysine residue. Each mature eIF‐5A molecule contains only one hypusine. Hypusine formation on eIF‐5A is essential for cell survival and proliferation. The biochemistry of hypusine formation has been actively investigated in a number of leading laboratories during the past decade. The precise functional role of eIF‐5A remains a mystery. This paper reviews recent progress in the study of the biochemistry of hypusine formation and offers speculation on the possible functio

ISSN:0009-4536    

DOI:10.1002/jccs.199900100

出版商:WILEY‐VCH Verlag    

年代:1999

数据来源: WILEY