Greater Inactivation Research Articles

Critical residues in D-amino acid oxidase. A pulse-radiolysis and inactivation study.

The enzyme D-amino acid oxidase and its apoenzyme have been irradiated at pH 5.5--10 under conditions designed to assess the inactivating effect of OH radicals and the selective free radicals Br2- and (SCN)2-. Near neutral pH, removal of the coenzyme FAD from the enzyme results in greater inactivation by selective free-radical attack. From pulse-radiolysis spectra, this increase is associated with attack on tyrosine and tryptophan residues in the protein. A large increase in inactivation of both the haloenzyme and apoenzyme by selective free-radical attack is seen with increasing alkalinity. This is consistent with attack on tyrosine being of major importance.

POST‐IRRADIATION INACTIVATION OF HORSERADISH PEROXIDASE

SUMMARY —Aqueous solutions of purified horseradish peroxidase lost enzymic activity not only during irradiation with gamma rays but also after irradiation. The higher the dose of irradiation, the greater the rate of post‐irradiation inactivation. Enzyme activity loss after irradiation increased at higher temperatures of post‐irradiation storage. Adjusting the pH of the irradiated enzyme solution to 9 resulted in greater inactivation than adjusting to pH 5 or 7. When the enzyme solution was diluted before irradiation the inactivation proceeded more rapidly after irradiation than in the more concentrated solution. When, however, the already irradiated enzyme was diluted, it was the concentrated enzyme solution that lost more activity. Glycerol added to irradiated enzyme diminished rate of inactivation. Irradiating a frozen enzyme solution resulted in very little or no loss of activity during post‐irradiation storage. Neither irradiated water nor irradiated enzyme solution affected the activity of non‐irradiated enzyme mixed with them. The following mechanism for the post‐irradiation inactivation of HRPO is proposed: A portion of the enzyme which is not inactivated during irradiation is modified so as to result in subsequent inactivation by reacting with itself.

Relationships of psychotomimetic to anti-serotonin potencies of congeners of lysergic acid diethylamide (LSD-25).

1. The psychotomimetic potency of 13 congeners of LSD-25 has been approximately determined in man. 2. With the exception of acetylation of the indole nitrogen, all the changes made in the LSD molecule reduced psychotomimetic potency. Bromination at carbon 2 caused the greatest inactivation. 3. High potency as a serotonin antagonist in isolated smooth muscle preparations was not correlated with high potency as a psychotomimetic. 4. The data do not support but do not disprove the “serotonin deficiency” hypothesis of the LSD psychosis.