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
✍ Scribed by E. Albert Zeller; Lorraine M. Clauss; John T. Ohlsson
- Publisher
- John Wiley and Sons
- Year
- 1974
- Tongue
- German
- Weight
- 1006 KB
- Volume
- 57
- Category
- Article
- ISSN
- 0018-019X
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✦ Synopsis
Abstract
Molecular activities, determined polarographically for the degradation of phenylalanine 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 van der Waals' radius of the substituent. This suggested that the large substituents cause the substrate molecules to be displaced from their normal (eutopic, productive) position at the active site, resulting in lower velocities. In analogous experiments with competitive inhibitors (ring‐substituted benzoic and phenylacetic acids), the logarithm of K~1~ was found to be a linear function of Hansch's hydrophobic constant π. 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. An 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.