Physicochemical and Kinetic Properties of Sulfohydrolases

The removal of neuraminyl residues from pure arylsulfohydrolase A by bacterial neuraminidase does not alter the specific activity, kinetic properties, and general stability but does change the elution profile through a DEAE-cellulose column (Fig. 1) and the electrophoretic mobility on a polyacrylamide gel (Graham and Roy, 1973 Farooqui and Srivastava, 1979). Das and Bishayee (1980) claimed that the treatment of partially purified sheep brain arylsulfohydrolase A with bacterial neuraminidase did not cause a 

The kinetics of arylsulfohydrolase A are quite complex, because the reaction velocity shows an abnormal relationship with the enzyme concentration and time of incubation (Roy, 1953 Baum and Dodgson, 1958) (Fig. 2), The anomalous reaction kinetics of arylsulfohydrolase A are manifested as a time-dependent decrease in hydrolytic rate during incubation with p-nitrocatechol sulfate, followed by a partial recovery of the initial rate. Baum and Dodgson (1958) have proposed that during the interaction of enzyme with substrate a new site capable of binding with substrate as well as the reaction product (nitrocatechol and sulfate) and certain other inhibitory compounds (phosphate 

The kinetic parameters of arylsulfohydrolase A with p-nitrocatechol sulfate are shown in Table 2. Optimal activity is at pH 5.0 with a value of 0.4 mM. This enzyme is strongly inhibited by sulfate, sulfite, and phosphate ions with Kj vines of 0.052, 0.026, and 0.034 mM, respectively (Table 3). Thus sulfite is the most potent inhibitor, followed by phosphate and sulfate. Such a powerful inhibition by sulfite suggests that this ion may be a transition-state analog intermediate of the arylsulfohydrolase A catalyzed reaction. This enzyme is also strongly inhibited by ascorbic acid 2-phosphate (Carlson et ah, 1976). The inhibition by ascorbic acid 2-phosphate is competitive with a Kj value of 0.3 xM. This metabolite binds very tightly to the enzyme molecule and may serve as controlling metabolite for arylsulfohydrolases. 

Kinetic Parameters of Human Aryl.sui.foiiydrola.se A wmi Different Substrates  

The mechanism of action of this activator has not been established, but it is known (Fischer and Jatzkewitz, 1978 Mitsuyama et al., 1985) that the activator forms an equimolar complex with cerebroside 3-sulfate prior to hydrolysis by arylsulfohydrolase A. Similar heat-stable activator proteins are also known for other acid hydrolases (Li and Li, 1983 Inui and Wenger, 1983 Wenger and Inui, 1984 Conzelmann et al., 1982 Christomanou and Kleinschmidt, 1985 Burg et al., 1985). It is becoming increasingly evident that many lysosomal hydrolases have specific activators, although some of these activators may be common to more than one enzyme (Li and Li, 1983, 1984 Li et al., 1985). The desulfation of cerebroside 3-sulfate also occurs in the absence of activator protein. In these experiments, Tween-20 or sodium 

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