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E T Kaiser

Publications and source records attributed to E T Kaiser.

143 records · Page 8Linked to original sources
PubMed1969

Effect of D2O on the carboxypeptidase-catalyzed hydrolysis of O-(trans-cinnamoyl)-L-beta-phenyllactate and N-(N-benzoylglycyl)-L-phenylalanine.

Solvent isotope effects have been examined for the action of the zinc-containing metalloenzyme carboxypeptidase A on ester and peptide substrates. The kinetic parameters for the carboxypeptidase-catalyzed hydrolysis of an ester, O-(trans-cinnamoyl)-L-beta-phenyllactate, in 0.05 M Tris-DCl buffer containing 0.5 M NaCl at pD 8.07 and 25 degrees were compared with those obtained from measurements done in 0.05 M Tris-HCl buffer containing 0.5 M NaCl at pH 7.52 and 25 degrees . A (k(cat))(H2O)/(k(cat))(D2O) ratio of approximately 2 was obtained. The value of the Michaelis constant K(m) was unaffected by the change in solvent as was the inhibition constant, K(i), found for the product, L-beta-phenyllactate, which is a competitive inhibitor. These results indicate that a catalytic step involving general base catalysis is probably important in the carboxypeptidase-catalyzed hydrolysis of an ester. A similar set of experiments carried out on the peptide substrate, N-(N-benzoylglycyl)-L-phenylalanine gave ambiguous results. The role of the zinc ion in the catalytic action of carboxypeptidase A can be considered in the light of these findings.

Carboxypeptidases↗
PubMedDate not supplied

Idealization of the hydrophobic segment of the alkaline phosphatase signal peptide.

Proteins secreted by prokaryotic cells are synthesized as precursors containing an amino-terminal extension sequence or signal peptide. Although these signal peptides share little primary sequence homology, recent studies suggest that they function via common pathways during the transport process and that a common element may reside in their secondary structural characteristics. We are investigating the role of an idealized hydrophobic sequence with high potential for alpha-helix formation in the Escherichia coli alkaline phosphatase signal peptide. Here, amino-acid substitutions were made using site-directed mutagenesis to produce a mutant signal sequence containing nine consecutive leucine residues in the hydrophobic core segment. Transport studies with this mutant precursor indicate that mature alkaline phosphatase is correctly targeted to the E. coli periplasm and that processing of the precursor to the mature form of the enzyme is extremely rapid. In contrast, processing is slowed when the mutant signal sequence is lengthened by the insertion of five additional leucine residues and one serine.

Alkaline Phosphatase↗