Abstract
Enzymes with nonspecific esterase activity were studied in carious and sound human dentine. The substrates were selected to represent various compounds containing ester bonds of fatty acids, phosphate or sulphate ester bonds, and glycosidic and peptide bonds. The water-extractable fraction of ground carious dentine revealed the highest enzyme activity towards 1- and 2-naphthyl acetate, 1-naphthyl valerate and 1-naphthyl propionate. By ultrasonic treatment of residue material, it was possible to prepare a further extract with considerable activity towards the substrates. Practically no enzyme activity towards these substrates was obtained from sound dentine samples by the methods used. Fractionation of water extracts of carious dentine by DEAE-cellulose chromatography revealed two enzymes (I and II) with esterolytic activity. One of the enzymes (II) was unspecific as regards to the bond being hydrolysed. The pH optimum of both the enzymes was 7.4. The value of the apparent Michaelis constant for enzyme I with 1-naphthyl acetate was 0.5 × 10 −4 M at pH 7.4. Hg 2+ ions, l-cysteine, and dithiothreitol (8.34 × 10 −4 M) totally inhibited the hydrolysis of 1-naphthyl acetate. Sodium taurocholate inhibited strongly the activity of enzyme I. By histochemistry the enzymes were localized in the tubules of carious dentine. No enzyme activity could be demonstrated in normal dentine. Gas-liquid chromatography on ether extracts of carious and sound dentine samples revealed that fatty acids of 18:0, 18:1, 16:0, 22:1 and 20:0 were the most abundant in carious, and those of 22:1, 21:0, 22:0 and 20:0, in sound dentine.
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