<Emphasis Type="SmallCaps">d</Emphasis>-Amino Acids in Animal Peptides

Summary. Secreted peptides from diverse sources have been found to contain a d-amino acid. From the sequence of cloned mRNAs coding for the precursors of such peptides it could be deduced that in all cases tested so far the d-amino acid in the final product is derived from the corresponding l-amino acid present in the primary product of translation. Enzymes catalyzing such an l- to d-isomerization in peptide linkage have been isolated from the venom of a spider and the skin secretions of frogs. Even though these are completely different proteins, the reaction mechanism is the same, namely a de-protonation/re-protonation of the α-carbon of an amino acid with concomitant inversion of the chirality. Sequences potentially coding for homologues of the frog enzyme are present in the genome of different vertebrate species.     

Substrate specificity and reaction mechanism of recombinant styrene oxide isomerase from Pseudomonas putida S12

To clarify the substrate specificity of the recombinant styrene oxide isomerase, various epoxides were subjected to the reaction. From the substituent effect on the rate of isomerization, the mechanism of the isomerase catalyzed reaction was estimated.     

Amperometric Determination of Serum Aldolase

Abstract

Serum Aldolase was determined by measuring the rate of decrease in the current generated by NADH at a platinum electrode. NADH is the cofactor for a dehydrogenase enzyme in the coupled enzyme reaction scheme used in the determination. Reducing agents in reconstituted lyophilized human serum did not interfere with the determination. Serum aldolase was accurately determined between 4 and 14 μ/ml which is the normal range in a healthy individual. The proposed amperometric method compares quite favorably with the spectrophotometric method.