Kinetic studies on the peroxidase activity of selenosubtilisin.

Selenosubtilisin, a semisynthetic selenoenzyme produced by chemical modification of the serine protease subtilisin, acts as a mimic of glutathione peroxidase, catalyzing the reduction of tert-butyl hydroperoxide by 3-carboxy-4-nitrobenzenethiol. To clarify the mechanism of action of this catalyst, detailed kinetic studies have been carried out. Thiol-mediated reduction converts the seleninic acid form of selenosubtilisin (ESeO2H) into a selenenyl sulfide (ESeSAr).

1H NMR spectroscopic studies of selenosubtilisin.

Anomalously low-field signals in 1H NMR spectra of serine proteases provide valuable information on the protonation state of the catalytic histidine residue. We have examined the pH dependence of the deshielded protons of three different oxidation states of selenosubtilisin, a semisynthetic selenoenzyme with significant peroxidase activity, in order to evaluate the influence of the selenium prosthetic group on the hydrogen-bonding network in the modified active site. In the spectra of the anionic seleninate and selenolate derivatives, two resonances were observed at 18.

In vivo catalysis of a metabolically essential reaction by an antibody.

We have established a growth selection requirement for a catalytic antibody with modest chorismate mutase activity. Conversion of (-)-chorismate into prephenate is the key step in the biosynthesis of the aromatic amino acids tyrosine and phenylalanine. Strains of the yeast Saccharomyces cerevisiae containing an insertion mutation in the structural gene for the enzyme chorismate mutase (EC 5.

Medium effects in antibody-catalyzed reactions.

Catalytic antibody technology has been used to explore the contribution of medium effects to the overall rate of an enzyme-catalyzed reaction. An antibody generated against a derivative of 2-acetamido-1,5-napthalenedisulfonate efficiently catalyzes the decarboxylation of 5-nitro-3-carboxybenzisoxazole. This unimolecular reaction is not susceptible to general acid-base catalysis but is highly sensitive to microenvironment; thus, it provides a simple chemical model for biologically important decarboxylations.

Yeast expression of a catalytic antibody with chorismate mutase activity.

The catalytic antibody 1F7 promotes the rearrangement of chorismate into prephenate. We cloned and sequenced the genes encoding this catalyst to determine the origin of the observed rates and specificity. The antibody cDNAs were modified and inserted into inducible expression vectors.

Antibody catalysis of carbon-carbon bond formation.

We have used rationally designed transition state analogues to generate antibodies that catalyse two important carbon-carbon bond forming reactions: a bimolecular Diels-Alder cycloaddition and a unimolecular Claisen rearrangement. Our tailored immunoglobulin catalysts (abzymes) exhibit all the properties of naturally occurring enzymes, including substantial rate accelerations, substrate specificity, and high regio- and stereoselectivity. As first generation abzymes are generally inferior to naturally occurring enzymes, we are also employing classical genetic selection strategies to augment their chemical efficiency.

Extending the chemistry of enzymes and abzymes.

Selective chemical modification can be used to create novel proteins, particularly enzymes and antibodies, with altered specificities and catalytic activities in vitro. Modification strategies now being developed should soon yield a wide spectrum of novel biomolecules whose activities are optimized for specific industrial processes or therapeutic applications.

Catalysis of concerted reactions by antibodies: the Claisen rearrangement.

Monoclonal antibodies were prepared against a transition state analog inhibitor of chorismate mutase (EC 5.4.99.

Use of directed mutagenesis to probe the role of tyrosine 198 in the catalytic mechanism of carboxypeptidase A.

Derivatization of Tyr198 in carboxypeptidase A (CPA) results in lowered catalytic activity toward peptide substrates (Cueni, L., and Riordan, J.F.

Site-directed mutagenesis shows that tyrosine 248 of carboxypeptidase A does not play a crucial role in catalysis.

The residue Tyr 248 of carboxypeptidase A (CPA) is thought to play a role in catalysis by contributing a proton to the incipient amine anion generated during cleavage of peptide substrates. To test this hypothesis we have modified the rat CPA cDNA by site-directed mutagenesis so that the codon for Tyr 248 is replaced by that for Phe. Here, we report the expression of the cDNAs for proCPA and its Tyr-to-Phe variant in yeast via the alpha-factor system.

Evidence for the general base mechanism in carboxypeptidase A-catalyzed reactions: partitioning studies on nucleophiles and H2(18)O kinetic isotope effects.

Methanol does not detectably compete with water in carboxypeptidase-catalyzed cleavage of any substrate, although it is preferentially reactive in a model for the proposed nucleophilic mechanism for the enzyme that involves an anhydride intermediate. To test for such a common intermediate in the cleavage of related peptide and ester substrates, a method has been developed to examine H2(16)O-H2(18)O kinetic isotope-partitioning effects. The finding that benzoylglycylphenylalanine has an isotope effect of 1.