Flow cytometric analysis of viability of bull sperm cells

Fluorescein diacetate and propidium iodide double fluorescence labeling of animal sperm cells in combination with 55 degrees C treatment for 15 min was used to monitor the viability and heat tolerance of sperm cells by flow cytometry. The applicability of the elaborated test to detect fertility differences has been shown on sperm samples obtained from bulls of known fertility values. According to preliminary examinations the method seems to be suitable to test the fertility of other male animals, too. The simplicity of the relatively quick procedure may provide a new screening method to qualify male animals before using their semen for large scale artificial insemination.

Study of the specificity of thrombin with tripeptidyl-p-nitroanilide substrates

The kinetic behaviour of human thrombin has been studied with 26 tripeptidyl-p-nitroanilide substrates protected at the N terminus and with 9 unprotected ones. By the regression analysis of experimentally determined 1/Km, kcat and kcat/Km values the individual contribution of each side chain of the various substrates to the kinetic parameters was calculated. The contributions to the kinetic parameters of the best substrates provide information about the structure of the binding site. The interaction of subsites S1 and P1, which determines primary specificity, proved to be marginal on the basis of contribution values, though it depends upon this contact whether the substrate is hydrolyzed at all. At subsite S2 proline appeared to be favourable. Subsite S3 plays an important role in efficiency. The best parameters were obtained here with the D configurations of bulky amino acid residues. The aromatic protecting groups applied did not improve the properties of substrates. BZDPhe-Pro-Arg-Nan was predicted by calculation to be better than the protected substrates assayed. The compound was synthesized and tested. Its experimentally determined 1/Km, 55.1 mM-1, was in good agreement with 50.9 mM-1 found by calculation.

Investigation of the substrate-binding site of trypsin by the aid of tripeptidyl-p-nitroanilide substrates

The kinetic parameters of the tryptic hydrolysis of tripeptidyl-p-nitroanilide substrates were determined and the data were studied by regression analysis. The sequence of substrates optimal from the viewpoint of kinetic constants 1/Km, kcat and kcat/Km was established and the influence of amino acid side chains on the binding and reactivity of substrates was calculated. At subsite P3 [notation of Schechter and Berger (1967) Biochem. Biophys, Res. Commun. 27, 157] polar side chains (Asn, D-Arg) are favourable as regards 1/Km, whereas hydrophobic side chains are preferred definitely from the viewpoint of catalytic efficiency, just as at subsite P2. In the side chain contributions, calculated for the kinetic parameters, the P3-S3 interaction predominates, in spite of the fact that the properties of the residue at subsite P1 decide whether hydrolysis occurs at all. The ZAsn-Ile-Arg-Nan sequence was predicted as a better substrate than those tested experimentally. The compound was synthesized, and the calculated value of its 1/Km (116.4 mM-1) was in a good agreement with the measured value (100.2 mM-1). Comparing the data obtained with trypsin with those observed with thrombin, elastase and subtilisin, we can establish that the homology of these enzymes can be characterized at each binding subsite by the aid of tripeptidyl-p-nitroanilide substrates. The quantities derived allow one to envisage a novel type of comparison of the proteases.

A method for designing peptide substrates for proteases. Tripeptidyl-p-nitroanilide substrates for subtilisin Carlsberg

1. The kinetic parameters of 25 peptidyl-p-nitroanilide substrates were investigated with subtilisin Carlsberg as model enzyme. 2. For a series of 12 substrates, the contribution of various side chains to the affinity constant was computed by regression analysis. From these contributions the sequence of a new and better substrate, N-benzyloxycarbonyl-arginyl-norleucyl-norleucyl-p-nitroanilide (Z-Arg-Nle-Nle-Nan) was predicted. The compound was synthesized and assayed. Its calculated 1/Km value, 43.5 mM-1, was in a good agreement with the value of 40.0 mM-1 that was determined experimentally. 3. On expanding the series to 19 substrates, it was found that the productivity of enzyme-substrate binding is influenced primarily by those subsites which have a significantly greater contribution to the affinity constants than others. 4. The additivity principle applied reasonably well for the contribution of individual side chains to the kinetic parameters. This fact suggests that regression analysis can be used for the prediction of the amino acid sequence of better substrates than those already tested, probably not only for subtilisin but also for other proteolytic enzymes.