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Allicin--diallyl thiosulfinate--is the main biologically active component of freshly crushed garlic. Allicin was synthesized as described elsewhere and was tested for its inhibitory ability against jack bean urease in 20 mM phosphate buffer, pH 7.0 at 22 degrees C. The results indicate that allicin is an enzymatic inactivator. The loss of urease activity was irreversible, time- and concentration dependent and the kinetics of the inactivation was biphasic; each phase, obeyed pseudo-first-order kinetics. The rate constants for inactivation were measured for the fast and slow phases and for several concentrations of allicin. Thiol reagents, and competitive inhibitor (boric acid) protected the enzyme from loss of enzymatic activity. The studies demonstrate that urease inactivation results from the reaction between allicin and the SH-group, situated in the urease active site (Cys592).

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4031reflected in part in the formation of metal complexes of anomalous structure in reversed micelle^.^^^^^ Acknowledgment. We are grateful to Professor J. H.Fendler of Texas A&M University for a kind gift of puflied pyranine.Maximal velocities of ultrasonic waves, as a function of the alcohol concentration in aqueous ethanolic medium, have been determined for solutions of D-ribose, 1-methyluracil, uridine, deoxyuridine, thymidine, and cytidine. The location of the maxima, and the velocities corresponding to these, are most sensitive to modifications in structure of the ribofuranose ring. The results are related to interaction of the sugar hydroxyls with water.Empirical and theoretical data are cited to support the approximation that shifts in strictly nonbonding valence orbital ionization potential are eight-tenths of corresponding shifts in core binding energy. This approximation is shown to be useful in the quantification of the bonding and antibonding character of molecular orbitals.

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