Interaction of ophidian L‐amino acid oxidase with its substrates and inhibitors: Role of molecular geometry and electron distribution. Communication 6 on ophidian L‐amino acid oxidases

Abstract

Molecular activities, determined polarographically for the degradation of phcnylalanine and 21 meta-and para-substituted derivatives by crystalline L-amino acid oxidase, yielded a linear Hammett plot of positive slope. However, the presence of large moieties in the para-position led to negative deviations which were linearly correlated with zlun der Waals' radius of the substitucnt. This suggested that the large substituents cause the substrate molcculcs to bc displaced from their normal (eutopic, productive) position at the active site, resulting in lowcr velocities. I n analogous experiments with competitive inhibitors (ring-substituted benzoic and phcnylacctic acids), the logarithm of Ki was found to be a linear function of Hansch's hydrophobic constant n. Lines of different slope characterized the meta-and para-derivatives, suggesting that the nature of the substituent affects the strength of hydrophobic binding, while the locus determines the orientation of the inhibitor on the active site. -4n analysis of the data reported here and in the literature for meta-and para-compounds supports the idea that the geometry of the ring-substituted substrate affects the orientation of the molecule on the active site, which may in turn determine which step of the reaction sequence becomes rate-limiting.Whenever a substrate molecule is bound to the active site of an enzyme, a catalytic event is presumed to take place. During the Fifties, however, an increasing number of observations obtained with several enzymes suggested the existence of enzyme-substrate complexes which are incapable of breaking down to products and free enzyme. A series of papers on the specificity of chymotrypsin by Niemann et al. and reviewed by Niemann in 1964 [5], stand out as milestones in this development.During the same period of time, a considerable body of experimental data on oxidative deamination was collected in this laboratory. This information was interpretable 1) Preliminary reports: 11-31, 2, 5th Communication: 141. 3, 4,

Amino Acid Chirality: Stereospecific Conversion and Physiological Implications

“…The oxidative deamination of LAA s by LAOs produces the corresponding α-keto acids, ammonia (NH 3 ) and hydrogen peroxide (H 2 O 2 ) ( Figure 2 B). First isolated by Blanchard et al in 1945, 40 and subsequently described by Zeller et al, 41 LAO is highly enriched in snake venoms, and much of the understanding of its mechanism of action has come from LAOs purified from these sources. The toxicity of venoms, in part, is attributable to the LAO activity that causes platelet aggregation.…”