Biomedical subjects

P Wirsching

Publications and source records attributed to P Wirsching.

9 recordsLinked to original sources

PubMed1997

On roads not taken in the evolution of protein catalysts: antibody steroid isomerases that use an enamine mechanism.

Reactive immunization has emerged as a new tool for the study of biological catalysis. A powerful application resulted in catalytic antibodies that use an enamine mechanism akin to that used by the class I aldolases. With regard to the evolution of enzyme mechanisms, we investigated the utility of an enamine pathway for the allylic rearrangement exemplified by Delta5-3-ketosteroid isomerase (KSI; EC 5.3.3.1). Our aldolase antibodies were found to catalyze the isomerization of both steroid model compounds and steroids. The kinetic and chemical studies showed that the antibodies afforded rate accelerations up to a factor of 10(4) by means of an enamine mechanism in which imine formation was the rate-determining step. In light of our observations and the enzyme studies by other workers, we suggest that an enamine pathway could have been an early, viable KSI mechanism. Although this pathway is amenable to optimization for increased catalytic power, it appears that certain factors precluded its evolution in known KSI enzymes.

Antibodies, Catalytic↗

PubMed1997

Making chemistry selectable by linking it to infectivity.

The link between recognition and replication is fundamental to the operation of the immune system. In recent years, modeling this process in a format of phage-display combinatorial libraries has afforded a powerful tool for obtaining valuable antibodies. However, the ability to readily select and isolate rare catalysts would expand the scope of library technology. A technique in which phage infection controlled the link between recognition and replication was applied to show that chemistry is a selectable process. An antibody that operated by covalent catalysis to form an acyl intermediate restored phage infectivity and allowed selection from a library in which the catalyst constituted 1 in 10(5) members. Three different selection approaches were examined for their convenience and generality. Incorporating these protocols together with well known affinity labels and mechanism-based inactivators should allow the procurement of a wide range of novel catalytic antibodies.

Antibodies, Catalytic↗

PubMed1995

Reactive immunization.

For almost 200 years inert antigens have been used for initiating the process of immunization. A procedure is now described in which the antigen used is so highly reactive that a chemical reaction occurs in the antibody combining site during immunization. An organophosphorus diester hapten was used to illustrate this concept coined "reactive immunization." The organophosphonate recruited chemical potential from the immune response that resembled the way these compounds recruit the catalytic power of the serine hydrolases. During this recruitment, a large proportion of the isolated antibodies catalyzed the formation and cleavage of phosphonylated intermediates and subsequent ester hydrolysis. Reactive immunization can augment traditional immunization and enhance the scope of catalytic antibody chemistry. Among the compounds anticipated to be effective are those that contain appropriate reactive functionalities or those that are latently reactive, as in the mechanism-based inhibitors of enzymes.

Animals↗

PubMed1995

Suppression of psychoactive effects of cocaine by active immunization.

Cocaine is a powerfully addictive substance and new strategies are needed to treat its abuse. Generating an active immunization to cocaine offers a means of blocking the actions of the drug by preventing it from entering the central nervous system, and should have fewer side effects than treatments based on manipulation of central neurotransmitter function. The design and preparation of a cocaine immunogen requires special regard for the stability of cocaine both free and as a haptenic determinant. Immunochemistry and a well defined behavioural model were brought together to address the problem of inactivation of the psychostimulant actions of cocaine. We report here that active immunization with a new, stable cocaine conjugate suppressed locomotor activity and stereotyped behaviour in rats induced by cocaine but not by amphetamine. Moreover, following acute injection of cocaine, levels of cocaine in the striatum and cerebellum of the immunized animals were lower than those of control animals. These results suggest that immunopharmacotherapy may be a promising means by which to explore new treatments for cocaine abuse.

Animals↗

PubMed1994

Direct selection for a catalytic mechanism from combinatorial antibody libraries.

Semisynthetic combinatorial antibody library methodology in the phage-display format was used to select for a cysteine residue in complementarity-determining regions. Libraries were panned with an alpha-phenethyl pyridyl disulfide that undergoes disulfide interchange. Out of 10 randomly picked clones, two contained an unpaired cysteine, one of which was studied. The antibody catalyzed the hydrolysis of the corresponding thioester where the electrophilic carbonyl occupies the three-dimensional space that was defined by the reactive sulfur atom during selection. The reaction operates by covalent catalysis. Although the steady-state rate enhancement relative to the activated thiol ester substrate is modest, hydrolysis of the acylated cysteine intermediate is remarkably efficient with a catalytic advantage of about four orders of magnitude. The results suggest that iterative mechanism-based selection procedures can recapitulate the enzymatic mechanisms refined through evolution.

Amino Acid Sequence↗

PubMed1991

An unexpectedly efficient catalytic antibody operating by ping-pong and induced fit mechanisms.

A transition state analogue was used to produce a mouse antibody that catalyzes transesterification in water. The antibody behaves as a highly efficient catalyst with a covalent intermediate and the characteristic of induced fit. While some features of the catalytic pathway were programmed when the hapten was designed and reflect favorable substrate-antibody interactions, other features are a manifestation of the chemical potential of antibody diversity. The fact that antibodies recapitulate mechanisms and pathways previously thought to be a characteristic of highly evolved enzymes suggests that once an appropriate binding cavity is achieved, reaction pathways commensurate with the intrinsic chemical potential of proteins ensue.

Acylation↗

PubMed1988

(Z)-3-(fluoromethyl)phosphoenolpyruvate: synthesis and enzymatic studies.

(Z)-3-(Fluoromethyl)phosphoenolpyruvate has been synthesized in nine chemical steps from glyoxylic acid. The compound is stable at pH 3, but at pH 8 it decomposes within seconds to give 2-oxo-3-butenoate. When 3-(fluoromethyl)phosphoenolpyruvate is added to a solution of phosphoenolpyruvate carboxylase or pyruvate kinase, the enzyme is inactivated over the course of an hour. Identical kinetics of inactivation are observed whether the reaction is initiated by addition of 3-(fluoromethyl)-phosphoenolpyruvate, preformed 2-oxo-3-butenoate, or 4-fluoro-2-oxobutanoate (which rapidly undergoes elimination of fluoride ion to form 2-oxo-3-butenoate). The inactivating species in all cases is believed to be 2-oxo-3-butenoate. The inactivation is completely prevented by the presence of dithiothreitol, which reacts rapidly with 2-oxo-3-butenoate. Studies with competitive inhibitors of both enzymes indicate that inactivation does not occur at the active site.

Carboxy-Lyases↗

PubMed1988

1-Carboxyallenyl phosphate, an allenic analogue of phosphoenolpyruvate.

1-Carboxyallenyl phosphate, the allenic homologue of phosphoenolpyruvate, has been synthesized in six steps. The key step in the synthesis is the isomerization of methyl 2-hydroxy-3-butynoate to the corresponding allenol and phosphorylation of this material. The allene is an excellent substrate for pyruvate kinase, undergoing reaction at more than half the rate of phosphoenolpyruvate. The allene is also a substrate for phosphoenolpyruvate carboxylase, being hydrolyzed by the enzyme rather than carboxylated. With both enzymes, the organic product is 2-oxo-3-butenoate, which gradually inactivates the enzymes by reaction with one or more sulfhydryl groups not at the active site.

Carboxy-Lyases↗

PubMed1985

(E)-3-Cyanophosphoenolpyruvate, a new inhibitor of phosphoenolpyruvate-dependent enzymes.

(E)-3-Cyanophosphoenolpyruvate has been synthesized by reacting dimethyl chlorophosphate with the potassium enolate of ethyl cyanopyruvate. The resulting trialkyl ester was deesterified with bromotrimethylsilane followed by potassium hydroxide. Subsequent treatment with Dowex-50-H+ resin and cyclohexylamine afforded the tricyclohexylammonium salt; only the E geometric isomer was obtained. This compound can be photoisomerized to a 70:30 E:Z mixture. (E)-3-Cyanophosphoenolpyruvate is an excellent competitive inhibitor of phosphoenolpyruvate carboxylase [KI(Mn2+) = 16 microM, KI(Mg2+) = 1360 microM], pyruvate kinase [KI(Mn2+) = 0.085 microM, KI(Mg2+) = 0.76 microM], and enolase [KI(Mn2+) = 360 microM, KI(Mg2+) = 280 microM]. The compound is a substrate for pyruvate kinase (Vmax approximately 1% of phosphoenolpyruvate rate), but not for the other two enzymes. No irreversible inactivation is observed with phosphoenolpyruvate carboxylase of pyruvate kinase.

Animals↗