A simple, rapid fluorimetric assay of amoxycillin in plasma

A method for estimation of amoxycillin in plasma is described, based on the formation of a fluorescent derivative which is measured in the presence of 2-methoxyethanol. Drugs commonly administered together with amoxycillin do not appear to interfere with the assay. Data on the sensitivity, accuracy and linearity of the assay are presented together with a comparison with the microbiological assay.

Active-site-directed alkylation of chymotrypsin by reagents utilizing various departing groups

Affinity-labeling reagents are useful for the inactivation of proteases in vivo but are apparently limited in application by the possibility of side reactions. In addition, increased specificity would be desirable. Substrate-derived chloromethyl ketones, one class of protease inhibitors, have been examined with the hope that replacement of the departing group halogen by other substituents might lead to improved inhibitor characteristics. Analogues of Z-Phe-Ch2X were synthesized in which X is a sulfonate or carboxylate substituent and examined as inactivators of chymotrypsin. The sulfonate esters were found to be more reactive than the previously studied halogen derivatives.

Combination antifungal therapy for cryptococcal meningitis

Two patients with Hodgkin's disease and cryptococcal meningitis are described. Both patients were treated with a combination of the two antifungal agents, amphotericin B and flucytosine. Nephrotoxicity was easily reversible in both patients and clinical improvement was seen with this combination therapy. Intrathecal therapy with amphotericin B was used in both patients. The optimal treatment of this disease may prove to be a combination of oral flucytosine, with amphotericin B given by intrathecal injection as well as rapid low dose intravenous injection.

13C high-resolution nuclear magnetic resonance studies of enzyme-substrate reactions at equilibrium. Substrate studies of chymotrypsin-N-acetyltyrosine semicarbazide complexes

N-Acetyl-L-tyrosine semicarbazide is hydrolyzed by chymotrypsin (EC 3.4.21.1) to N-acetyl-L-tyrosine and semicarbazide. If a high concentration of semicarbazide is present, the equilibrium for the reaction can be shifted from hydrolysis to synthesis. Using N-acetyl-L-[(13)C]tyrosine enriched at the carboxyl carbon and high concentrations of semicarbazide hydrochloride, we have studied the enzyme-substrate complex of N-acetyl-L-[(13)C]tyrosine semicarbazide and chymotrypsin A(delta) by (13)C nuclear magnetic resonance. We observe no shift within the experimental accuracy of +/-0.05 ppm as the fraction of substrate bound is changed from 0.17 to 0.70. Since E + S right arrow over left arrow ES is in fast exchange on the nuclear magnetic resonance time scale, it is possible to show that when the substrate is bound to the enzyme in the Michaelis complex, the (13)C resonance is shifted less than 0.1 ppm, indicating that negligible substrate strain occurs in this complex at the site of enzymatic attack. These experiments demonstrate the application of nuclear magnetic resonance to the study of particular states along the reaction pathway for enzyme-substrate reactions at equilibrium.

Letter: Current practice in tetanus prophylaxis

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Affinity labelling of proteinases with tryptic specificity by peptides with C-terminal lysine chloromethyl ketone

Methods are described for the synthesis of peptides terminating in Lys-CH(2)Cl. The products were examined as affinity labels for several enzymes of trypsin-like specificity which are resistant to Tos-Lys-CH(2)Cl. In part, the inertness of the latter may be due to the sulphonamide group, since Z-Lys-CH(2)Cl was more effective. However, a number of tripeptides with C-terminal Lys-CH(2)Cl were superior in their ability to inactivate subtilisin, thrombin and plasma kallikrein. The possibility of developing enzyme-specific reagents selective for members within the trypsin-like group is demonstrated by Ala-Phe-Lys-CH(2)Cl, which readily inactivates plasma kallikrein but not thrombin.