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L Wicker

Publications and source records attributed to L Wicker.

13 recordsLinked to original sources
PubMed2000

Separation of thermostable pectinmethylesterase from marsh grapefruit pulp.

A rapid, ion-exchange method that isolates thermostable pectinmethylesterase (TS-PME) from Marsh grapefruit pulp is presented. TS-PME was selectively extracted with 1 M NaCl and equilibrated at low pH (3.1 +/- 0.04). After dilution to a final concentration of 50 mM acetate buffer, pH 5.5, and 0.1, 0.25, or 0.5 M NaCl, the extract was applied to an ion-exchange column without ammonium sulfate precipitation and dialysis. The percent yield varied from an average of 70% (0.1 M NaCl) to 14% (0.5 M NaCl), with a specific activity of >400 U/mg protein in the latter sample. TS-PME activity of some column fractions varied compared with crude extracts before column separation. Some fractions lost thermostability after separation if loaded at 0.1 M or 0.25 M NaCl. In extracts that were loaded at 0.5 M NaCl, the TS-PME activity was significantly higher than that observed in the heated crude extracts. Ion-exchange chromatography may have separated an unidentified protective factor in PME fractions.

Carboxylic Ester Hydrolases↗
PubMed2000

Role of cations in the catalysis of thermostable pectinmethylesterase extracted from Marsh grapefruit pulp.

The de-esterification of high methoxyl pectin by thermostable pectinmethylesterase (TS-PME) from Marsh grapefruit was studied at pH 7.5, in a temperature range between 25 degrees and 50 degrees C and in the presence of various cations. Arrhenius plots were constructed for CaCl(2) (5 to 20 mM), SrCl(2) (5 to 20 mM), and spermidine (2.5 to 10 mM) added reactions. Enthalpy (DeltaH()) and entropy (DeltaS()) of activation changed with cation type and concentration. The presence of cations modified the free energy of the resulting enzyme/substrate complex. The entropy of activation was positive at all concentrations of CaCl(2) studied, and negative in the same concentration range with SrCl(2). Reactions with spermidine showed negative entropy of activation at concentrations <5 mM and positive values of entropy at higher concentrations.

Carboxylic Ester Hydrolases↗
PubMed2000

Aqueous apple flavoring in breast muscle has physical, chemical, and sensory properties similar to those of phosphate-marinated controls.

Marinades containing 0, 0.4, 0.8, and 1.2% apple flavoring were examined to determine the effect of an aqueous apple flavoring on the quality and sensory characteristics of boneless, skinless chicken breast. Marinade pickup and purge loss increased significantly with an increase of apple flavoring in marinades. Incorporation of apple flavoring in the marinades did not affect cook loss of the treatments, except for breast marinated in 1.2% apple flavor, which had higher cook loss. Apple flavoring did not affect final product yield of marinated breast. Shear values were similar for all treatments except marinades with 0.8% apple flavoring, which had lower shear values. Participants detected increases in fruity flavor with an increase of apple flavoring in the marinade. Products containing no apple flavoring were rated as "like moderately" to "like slightly." Products with 0.4% apple flavoring were rated "like slightly," and degree of liking declined to "neither like nor dislike" as apple flavoring increased. Incorporation of acceptable levels of apple flavoring is limited to 0.4%.

Animals↗
PubMed1999

Kinetic compensation and the role of cations in pectinesterase catalysis.

The catalytic rate constant of thermostable pectinesterase (TS-PE) from Marsh grapefruit pulp was determined at pH 7 at temperatures between 25 and 60 degrees C. TS-PE activity was measured at NaCl concentrations of 0.05, 0.10, 0.15, and 0.20 M and at CaCl(2) concentrations of 0.005, 0.010, 0.015, and 0.020 M. For sodium- and calcium-added conditions, the kinetic functions of this reaction agreed with kinetic compensation relations. The isokinetic temperatures for sodium- and calcium-added conditions were 327.8 and 312.4 K, respectively. Different isokinetic temperatures and compensation parameters suggest that sodium and calcium uniquely affect TS-PE catalysis. This is the first demonstration of kinetic compensation in an enzyme-catalyzed reaction.

Calcium Chloride↗
PubMed1996

Genetic control of giant perivascular space formation in the thymus of NOD mice.

The immune system of NOD mice exhibits several anomalies, one being the intrathymic formation of giant perivascular spaces (PVSs) filled with mature thymocytes and some B-cells, intermingled within a network of extracellular matrix. The abnormal retention of thymocytes on their way to the periphery could have a profound impact on the nature of the exported cells and the regulation of autoimmune events. In the present study, we evaluated the appearance of this defect into F1 hybrids, the association with some of the known diabetes susceptibility loci (Idd genes) in a panel of NOD and reciprocal C57BL congenic strains, and the relative contribution of epithelial versus hematopoietic stroma. The analysis of F1 hybrid thymuses reveals a dominant expression of thymic giant PVS that is only marginally influenced by the outcross strain. Moreover, giant PVS expression in major histocompatibility complex (MHC) and Idd congenic mice is determined by the genetic background. All of the NOD congenics express the anomaly, irrespective of the Idd resistance alleles that have been introgressed, whereas none of the C57BL congenic mice present abnormal PVS. Finally, the expression of giant PVS in parental --> F1 bone marrow chimeras is predominantly controlled by the thymic NOD-derived hematopoietic microenvironment. In conclusion, the giant PVS formation in the NOD mouse thymus is a dominantly inherited anomaly associated with hematopoietic-derived tissue and with non-MHC genes. The exact contribution of PVS to the autoimmune process remains to be definitively established.

Animals↗
PubMed1995

Autoimmunity.

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Animals↗
PubMed1990

The role of CD4+ helper T cells in the destruction of microencapsulated islet xenografts in nod mice.

Islet transplants for large numbers of patients with diabetes will require xenografts. Microencapsulation is an appealing method for islet xenografting. However, graft function has been limited by a cellular reaction, particularly intense in spontaneously diabetic, NOD mice. The purpose of this study was to elucidate the mechanism of this reaction. Poly-1-lysine-alginate microcapsules containing 4000-12,000 dog or 1800-2000 rat islets were xenografted intraperitoneally into streptozotocin (SZN)-diabetic C57BL/6J and NOD mice, with or without recipient treatment with GK 1.5 (anti-CD4 monoclonal antibody) (20-30 microliters i.p. every 5 days, begun on day -7. Grafts were considered technically successful if random blood glucose (BG) was normalized (less than 150 mg/dl) within 36 hr. Graft failure was defined as BG greater than 250 mg/dl. Dog and rat islets in microcapsules normalized BG in both SZN and NOD mice within 24 hr routinely. Empty microcapsules and GK 1.5 treatments alone did not affect BG. NODs destroyed both microencapsulated dog and rat islets more rapidly than did SZN-diabetic mice (P less than .01). Graft biopsies showed an intense cellular reaction, composed of lymphocytes, macrophages and giant cells, and no viable islets. GK 1.5 treatment significantly prolonged both dog-to-NOD and rat-to-NOD grafts (P less than 0.01). Biopsies of long-term functioning grafts (on days 65-85) demonstrated viable islets and no cellular reaction around microcapsules; 1/4 rat and 1/8 dog islet xenografts continued to function indefinitely in NOD recipients, even after cessation of GK 1.5 therapy. Prediabetic NODs receiving encapsulated dog or rat islets mounted a moderate cellular reaction to grafts. Empty microcapsules excited no cellular reaction in diabetic or prediabetic NODs. We conclude that the NOD reaction to microencapsulated xenogeneic islets is helper T cell-dependent, and that the target of this reaction is not the microcapsule itself, but the donor cells within.

Animals↗
PubMed1990

Microencapsulated dog and rat islet xenografts into streptozotocin-diabetic and NOD mice.

Microencapsulation is an appealing method for islet xenografting. However, graft failure has been related to a cellular reaction, particularly intense in spontaneously diabetic, NOD mice. The goal of this study was to characterize this reaction. Poly-l-lysine-alginate microcapsules containing dog or rat islets were xenografted intraperitoneally into streptozotocin (SZN)-diabetic C57BL/6J and spontaneously diabetic NOD mice, with or without recipient treatment with GK 1.5 (anti-CD4 monoclonal antibody). Both dog and rat islets in microcapsules normalized blood glucose (BG) routinely in both SZN and NOD mice within 24 hours. Empty microcapsules and GK 1.5 treatment did not affect BG. NODs destroyed both microencapsulated dog and rat islets more rapidly than did SZN-diabetic mice (P less than 0.01). Graft biopsies showed an intense cellular reaction and no viable islets. GK 1.5 treatment significantly prolonged both dog-to-NOD and rat-to-NOD grafts (P less than 0.01). Biopsies of long-term functioning grafts (on days #70-#95) demonstrated viable islets and no cellular reaction. In prediabetic NODs, encapsulated dog and rat islets elicited a moderate cellular reaction. Empty microcapsules excited no cellular reaction in either diabetic or prediabetic NODs.

Animals↗
PubMed1988

The binding of 8-anilino-1-naphthalene sulfonate (ANS) to fish myosin and the effect of salts on the thermal transitions of fish myosin-ANS complex.

Myosin prepared from tilapia (Serotherodon aureus) was complexed with 8-anilino-1-naphthalene sulfonate (ANS) and continuously heated at 1 degree C/min. A large increase in fluorescence was observed with a transition temperature of 34 degrees C. The effect of several salts on the transition temperature was tested. A plot based on the equation of E. E. Schrier and E. B. Schrier [(1967) J. Phys. Chem. 71, 1851-1860] gave a value of less than or equal to 500 cal/mol-deg for the change in enthalpy per residue due to exposure to solvent. The ratio of hydrophobic group to amide group exposure to solvent was intermediate compared with the ratio of RNase and gelatin. Fluorescence titrations yielded one high affinity site with a Kb of 2 X 10(6) M-1 and at least 200 low affinity sites with an average value of 1 X 10(5) M-1. The parameters did not change significantly with temperature. We propose that the increase in ANS fluorescence reflects changes in conformation of myosin as monitored by these low affinity sites, resulting in an increase in surface hydrophobicity and representing a small enthalpic change in the conformation of the myosin molecule. As a consequence, the change in conformation accelerates polymerization of myosin oligomers.

Anilino Naphthalenesulfonates↗
PubMed1982

Immunological focusing by th mouse major histocompatibility complex: mouse strains confronted with distantly related lysozymes confine their attention to very few epitopes.

The gallinaceous lysozymes are a family of antigens that are distantly related to mouse lysozyme. A T cell-dependent proliferation assay was used to characterize the spectrum of reactivities to lysozyme determinants in B10-congenic mice. Cross-reactivity studies using a panel of species variant lysozymes to stimulate lymph node cells from chicken egg white lysozyme- and ring-necked pheasant egg white lysozyme-primed B10.D2 mice indicated a preferential focusing of T cell reactivity onto a single determinant containing amino acids 113-114. These data, in conjunction with results obtained by priming with cyanogen bromide cleavage fragments of lysozymes, suggested that a site commmon to the L3 region (amino acids 106-129) of all the lysozymes tested was a preferential anchorage site for I region-encoded Ia molecules on H-2d antigen-presenting cells, leading to the limited display of a determinant containing residues 113-114. Priming with L2H (amino acids 13-105), a peptide containing the major epitopes recognized by B10. A and B10 mice, failed to stimulate any T cell proliferation by B10.D2 lymph node cells. Thus, it appears the Ia molecules in any one mouse strain attach to very few sites on lysozyme to effectively display antigenic determinants for T cell activation. This result points to a model of limited determinant selection even on a very "foreign" antigen based upon a shortage of appropriate amino acid residues usable by Ia antigen-presenting structures of a strain.

Animals↗