silicotungstic, phosphotungstic, and phosphomolybdic. These are (i) anticoagulant activity in vitro and in vivo (3); (ii) the ability to elicit the appearance of plasma clearing factor activity (3). The work discussed in this report demonstrates that these inorganic substances also resemble heparin in their ability to inhibit crystalline beef pancreas ribonuclease. In addition, dextran sulfate (4) and two sulfated pectic acid derivatives which possess anticoagulant activity (5) were also found to be potent ribonuclease inhibitors.Ribonuclease activity was determined by the spectrophotometric method of Kunitz (6) at pH 5.0. Each of the substances was brought to pH 5.0 before addition to the test system. The polyacids were commercial products.The data given in Table 1 demonstrate that all five of the polyacidic substances inhibit ribonuclease activity under these conditions. Relative inhibitory activity seems to fall in the general order: dextran sulfate > sulfated pectic acid amide > sulfated pectic acid methyl ester > silicotungstate > phosphomolybdate. In general, the sulfated polysaccharides were more active than the inorganic polyacids.Since pepsin has the lowest isoelectric point of any known protein (7), a sample was inactivated by alkali treatment (8), then adjusted to pH 5.0. This material showed very little ribonuclease inhibitory activity. This result is in marked contrast to the inhibition obtained by Vandendriessche (2) with polyaspartic acid and indicates that proper spacing of Table 1. Inhibition of ribonuclease (RNase) by polyacids. Decrease inA00 A Relative Amt. RNA between Re added added 1 and RNase (mg/4 ml) (mg/4 ml) 5 min. activity after (%) mixing Silicotungstate None 0.9 0.038 100 0.20 0.9 0.002 5 0.10 0.9 0.008 21 0.08 0.9 0.014 37 0.06 0.9 0.021 55 0.04 0.9 0.034 89 0.02 0.9 0.035 92 Phosphomolybdate None 0.9 0.035 100 0.6 0.9 0.035 100 0.8 0.9 0.023 66 0.8 1.2 0.034 97 Dextran sulfate 0.2 0.9 0.001 3 0.1 0.9 0.004 11 0.02 0.9 0.012 34 Sulfated pectic acid methyl ester None 1.2 0.036 100 0.10 1.2 0.012 34 0.05 1.2 0.025 71 Sulfated pectic acid amide silicotungstic, phosphotungstic, and phosphomolybdic. These are (
i) anticoagulant activity in vitro and in vivo (3); (ii) the ability to elicit the appearance of plasma clearing factor activity (3).The work discussed in this report demonstrates that these inorganic substances also resemble heparin in their ability to inhibit crystalline beef pancreas ribonuclease. In addition, dextran sulfate (4) and two sulfated pectic acid derivatives which possess anticoagulant activity (5) were also found to be potent ribonuclease inhibitors. Ribonuclease activity was determined by the spectrophotometric method of Kunitz (6) at pH 5.0. Each of the substances was brought to pH 5.0 before addition to the test system. The polyacids were commercial products.The data given in Table 1 demonstrate that all five of the polyacidic substances inhibit ribonuclease activity under these conditions. Relative inhibitory activity seems to fall in the general order: dextran...
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