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T Norin

Publications and source records attributed to T Norin.

At least 19 recordsLinked to original sources
PubMed2001

Improved enantioselectivity of a lipase by rational protein engineering.

A model based on two different binding modes for alcohol enantiomers in the active site of a lipase allowed rational redesign of its enantioselectivity. 1-Halo-2-octanols were poorly resolved by Candida antarctica lipase B. Interactions between the substrates and the lipase were investigated with molecular modeling. Unfavorable interactions were found between the halogen moiety of the fast-reacting S enantiomer and a region situated at the bottom of the active site (stereoselectivity pocket). The lipase was virtually mutated in this region and energy contour maps of some variants displayed better interactions for the target substrates. Four selected variants of the lipase were produced and kinetic resolution experiments were undertaken with these mutants. Single point mutations gave rise to one variant with doubled enantioselectivity as well as one variant with annihilated enantioselectivity towards the target halohydrins. An increased volume of the stereoselectivity pocket caused a decrease in enantioselectivity, while changes in electrostatic potential increased enantioselectivity. The enantioselectivity of these new lipase variants towards other types of alcohols was also investigated. The changes in enantioselectivity caused by the mutations were well in agreement with the proposed model concerning the chiral recognition of alcohol enantiomers by this lipase.

Binding Sites↗
PubMed2001

Resolution of an iridoid synthon, gastrolactol, by means of dynamic acetylation and lipase-catalyzed alcoholysis.

A short synthetic route to asymmetric iridoids was developed. The three key steps were an intramolecular [4 + 2] cycloaddition reaction of an enamine derivative of 8-oxocitral (2), a dynamic acetylation, and an enzymatic resolution of the gastrolactyl acetates 5a and 5b, iridoids with three stereocenters. Some regio- and stereoselective heterogeneous catalytic hydrogenations of double bonds in iridoid aglucones were discussed.

Acetylation↗
PubMed2000

Mass transport limitations reduce the effective stereospecificity in enzyme-catalyzed kinetic resolution.

[reaction-see text] The kinetic resolution of seudenol catalyzed by Candida antarctica lipase B in hexane was investigated. Large differences in reaction rate and stereospecificity were observed when different enzyme preparations were used. These differences were ascribed to mass transport limitations which reduced both reaction rate and stereospecificity. Lyophilized enzyme preparations were more apt to give this problem than immobilized preparations. Further, low substrate concentrations enhanced the effect. Thus, high alcohol concentrations and enzyme immobilization can be recommended.

Candida↗
PubMed2000

An active-site titration method for lipases.

A method for active-site titration of lipases has been developed based on irreversible inhibition by methyl p-nitrophenyl n-hexylphosphonate. This method was applied to five lipases displaying from minor to pronounced interfacial activation. Soluble and immobilized lipases were successfully titrated in aqueous media. A low concentration of sodium dodecyl sulfate was needed for lipases displaying pronounced interfacial activation. The carrier of some of the immobilized preparations adsorbed part of the produced p-nitrophenolate. This problem could be solved by extracting the p-nitrophenolate after inhibition. The method was extended to apolar organic solvents in the case of immobilized lipase preparations.

Binding Sites↗
PubMed1998

Molecular modeling of the enantioselectivity in lipase-catalyzed transesterification reactions.

Two strategies based on the use of subsets for calculating the enantioselectivity in lipase-catalyzed transesterifications using the CHARMM force field were investigated. Molecular dynamics was used in our search for low energy conformations. Molecular mechanics was used for refining these low energy conformations. A tetrahedral intermediate with a rigid central part was used for mimicking the transition state. The energy differences between the transition states of the diastereomeric enzyme-substrate complexes were calculated. The way of defining the subsets was based on two fundamentally different strategies. The first strategy used predefined parts of the enzyme and the substrate as subsets. The second approach formed energy-based subsets, varying in size with the substrates studied. The selection of residues to be included in these energy-based subsets was based on the energy of the interaction between the specific residue or water molecule and the transition state. The reaction studied was the kinetic resolution of secondary alcohols in transesterifications using the Candida antarctica lipase B as chiral biocatalyst. The secondary alcohols used in the study were 2-butanol, 3-methyl-2-butanol, and 3,3-dimethyl-2-butanol.

Binding Sites↗
PubMed1996

A structural basis for enantioselective inhibition of Candida rugosa lipase by long-chain aliphatic alcohols.

Molecular modeling showed that the enantiomers of heptyl 2-methyldecanoate are productively bound to the active site of Candida rugosa lipase in quite different conformations. The fast-reacting S-enantiomer may well occupy the previously identified acyl-binding tunnel in the active site of the lipase. By contrast, the slow-reacting R-enantiomer must be bound to the active site, leaving the tunnel empty to allow the formation of two catalytically essential hydrogen bonds between His 449 of the catalytic triad and the transition state of the catalyzed reaction. This information enables us to propose a molecular mechanism explaining how long-chain aliphatic alcohols act as enantioselective inhibitors of this lipase in the resolution of 2-methyldecanoic acid. Long-chain aliphatic alcohols may coordinate to the acyl-binding tunnel of the C. rugosa lipase, thereby selectively inhibiting the turnover of the fast-reacting S-enantiomer, thus resulting in a lowered enantioselectivity in the resolution.

Alcohols↗
PubMed1995

A cohort study with regard to the risk of haematological malignancies in patients treated with x-rays for benign lesions in the locomotor system. I. Epidemiological analyses.

Roentgen treatment for painful benign conditions in the locomotor system as arthrosis and spondylosis was in Sweden very common up to the beginning of the 1960s. The mode of treatment differed from the British ankylosing spondylitis series as smaller parts of the red bone marrow were exposed and smaller doses were applied. A cohort of 20,024 such patients treated 1950-1964 at two hospitals in northern Sweden was analysed with regard to the risk of haematological malignancies. Average factors for conversion of prescribed skin doses to mean absorbed red bone marrow doses were estimated on random samples of the different treatment sites and then applied on the cohort in its whole. The standard incidence ratio (SIR) for leukaemia was 1.18 (95% CI: 0.98-1.42) and the standard mortality ratio (SMR) 1.25 (0.99-1.45). In the highest dose group (mean absorbed red bone marrow dose > 0.5 Gy) the corresponding values were 1.40 (1.00-1.92) and 1.50 (1.08-2.04). In the mortality analysis also a slightly increased myeloma risk was noted with SMR = 1.20 (0.99-1.56). Extension of the cohort and nested case-control studies are under progress.

Adult↗
PubMed1994

Computer modeling of substrate binding to lipases from Rhizomucor miehei, Humicola lanuginosa, and Candida rugosa.

The substrate-binding sites of the triacyl glyceride lipases from Rhizomucor miehei, Humicola lanuginosa, and Candida rugosa were studied by means of computer modeling methods. The space around the active site was mapped by different probes. These calculations suggested 2 separate regions within the binding site. One region showed high affinity for aliphatic groups, whereas the other region was hydrophilic. The aliphatic site should be a binding cavity for fatty acid chains. Water molecules are required for the hydrolysis of the acyl enzyme, but are probably not readily accessible in the hydrophobic interface, in which lipases are acting. Therefore, the hydrophilic site should be important for the hydrolytic activity of the enzyme. Lipases from R. miehei and H. lanuginosa are excellent catalysts for enantioselective resolutions of many secondary alcohols. We used molecular mechanics and dynamics calculations of enzyme-substrate transition-state complexes, which provided information about molecular interactions important for the enantioselectivities of these reactions.

Binding Sites↗
PubMed1994

Enhanced stereoselectivity in pig liver esterase catalysed diester hydrolysis. The role of a competitive nucleophile.

The enantioselectivity of pig liver esterase catalysed hydrolysis of cis-N-benzyl-2,5-bis(methoxy-carbonyl)pyrrolidine (1) has previously been shown to be very dependent on the reaction conditions. Hydrolysis performed in media buffered with tris(hydroxymethyl)aminomethane (Tris) afforded a monoester with much higher optical purity than hydrolysis in media without Tris. Detailed product studies in a Tris-buffered medium have been performed using NMR-techniques and a 13C-labelled ester. The NMR-studies revealed the presence of (2S,5R)-N-benzyl-2-methoxycarbonyl-5-[[[2-hydroxy-1,1- bis(hydroxymethyl)ethyl]amino]carbonyl]pyrrolidine (4) as an intermediate, which together with the isolated product (2S,5R)-N-benzyl-2-carboxy-5-[[[2-hydroxy-1,1-bis(hydroxymethyl) ethyl]amino]carbonyl]pyrrolidine (3) suggested Tris as a competitive nucleophile to water. The increased enantioselectivity seen in the produced (2R,5S)-N-benzyl-2-methoxy-carbonyl-5-carboxypyrrolidine (2) was explained by the preference of Tris to react faster with one of the diastereomeric acyl enzymes over the other.

Animals↗
PubMed1989

Perioperative adjuvant chemotherapy in breast cancer. The Scandinavian Adjuvant Chemotherapy Study 1.

In a randomized study of operable primary breast cancer patients initiated January 1965, 507 patients received one single course with cyclophosphamide 5 mg/kg/day for six days, first dose given immediately after mastectomy. The 519 control patients received no adjuvant chemotherapy. In other respects both groups were treated equally. Median follow-up time is 17.1 years. In terms of relapse-free percentage, the difference between the groups after 20 years is 13.5% in favour of the cyclophosphamide group. The difference is statistically highly significant. This benefit is observed in node positive as well as in node negative patients, and over as well as under 50 years. The immediate side effects of the cyclophosphamide course have been very moderate. No late complications have been observed. In a parallel randomized study with 110 patients where the same course was given 2-4 weeks after mastectomy, no benefit could be observed.

Aged↗
PubMed1986

Treatment of node-negative breast cancer patients with short course of chemotherapy immediately after surgery.

In our first study, one short course of chemotherapy (cyclophosphamide, 5 mg/kg/day for 6 days iv) was given perioperatively to 507 patients with operable primary breast cancer; there were 519 control subjects. Randomization was done by telephone from the operating theater, and stratification was by hospital only. The side effects were negligible. With 20-year follow-up, the relapse rate was 60.5% in the control group and 48% in the treatment group (P less than 0.001). The overall survival benefit was marginally significant, but with correction for deaths not related to cancer, P was less than 0.02. A total of 309 patients in the treatment group and 301 in the control group were histologically node negative. The observed benefit in this subgroup was as good as in the node-positive subgroup, but the relapses were too few for testing of meaningful significance. In our second study, all patients received one short perioperative course, and the node-positive patients were randomized between control or continued chemotherapy for 1 year. This improved the beneficial results but also considerably increased the side effects.

Adult↗
PubMed1985

Short perioperative versus long-term adjuvant chemotherapy.

A single course of cyclophosphamide IV 5 mg/kg daily for 6 days was given immediately after mastectomy to 507 patients (519 randomized controls). The relapse-free rates were significantly increased, and after 16 years the difference was 12%. In a parallel series the same adjuvant course was given 2-4 weeks after mastectomy to 52 patients (58 randomized controls). No effect of this delayed course was found. In a second study a short multidrug course was given to all patients immediately after mastectomy. One-half of the axillary node-positive cases were randomized to continue with IV CMF for 1 year. The preliminary observations show that the prolonged treatment improved the relapse-free rates significantly during the first few years. One year after mastectomy the difference was 10%; after 2 years, 9%; after 3 years, 11%; and after 4 years, 9%. The side-effects of the short course were negligible, but the side-effects of prolonged treatment were considerable and increased with increasing treatment duration. More trials are needed to find the optimum duration of adjuvant chemotherapy.

Antineoplastic Agents↗
PubMed1982

Treatment of early localized breast cancer in elderly patients by Tamoxifen.

Twenty-seven early localized breast cancer cases in elderly patients, 21 stage I and six stage II, were treated with Tamoxifen only. In 15 cases there was complete radiological remission and in seven cases partial remission or growth arrest. Five cases did not respond to treatment. Tamoxifen seemed to be a useful alternative treatment for this group of patients. Possibly tumour mass and growth rate may affect the response to antioestrogen treatment.

Aged↗
PubMed1980

Surface immunoglobulins on Burkitt's lymphoma biopsy cells from 91 patients.

One hundred and fourteen biopsies from 91 cases of African Burkitt's lymphoma were examined by immunofluorescence methods for the presence of surface-associated mu, gamma, delta, kappa and lambda chains, as well as for the Fc region of gamma chains and for beta1C. Only 5% of the biopsies were surface-Ig-negative; 18% were negative for mu chains and 61% for gamma chains. Delta chain staining was absent, or borderline in a few tumors. Mu chains, gamma chains in a few highly reactive tumors and, in many cases, the predominant light chain seemed to be clonal markers. They gave no convincing evidence of more than one cell clone, either within single tumors or within syn- or metachronous tumors in one individual. Gamma chains in moderately stained tumors, Fc and beta1C correlated with each other and the first two reactivities decreased after incubation at low pH, indicating that their presence resulted from outside coating of the cells. The results indicated that one clone of B cells is involved in Burkitt's lymphoma in the large majority of cases. This clone is in a state of differentiation at which surface delta chains are not expressed. No prognostic information resulted from the analysis of the markers studied.

Biopsy↗
PubMed1979

Epstein-Barr virus-specific antibody-dependent cellular cytotoxicity in patients with Burkitt's lymphoma.

Coded sera from 54 patients with African Burkitt's lymphoma (BL) were titrated for antibodies against an Epstein-Barr virus (EBV)-induced membrane antigen in the antibody-dependent cellular cytotoxicity (ADCC) assay. The titers were then correlated with the progression of lymphoma growth following chemotherapy. In 74% of the patients with high ADCC titers (greater than 3,840), lymphomas showed partial or complete regression following therapy. In the medium-titered group (240-3,840), 36% of the lymphomas showed some response to therapy, while only 29% of the lymphomas in the low group (less than 240) responded to treatment. These preliminary results indicated that, as previously reported for patients with nasopharyngeal carcinoma, ADCC titers may be a prognotic value in patients with this EBV-associated disease. In an attempt to determine the identity of the ADCC antigen, some of these sera were examined for antibody to the four major MA components so far identified in the membrane of EBV-infected Raji cells. Sera with high ADCC titers in general contained antibody to the four major MA components, while low-titered sera usually contained antibody to three or less of these proteins. There were exceptions to this pattern, however, indicating that the ADCC antigen might differ from the four EBV-induced membrane components so far identified.

Antibodies, Viral↗