The anomalous kinetics of sulphatase A.


where R-OH is a phenol. Rather later it was shown (Mehl & Jatzkewitz, 1964, 1968) that its physiological role was the hydrolysis of galactose 3-sulphate residues in cerebroside sulphate and other sulphated galactolipids. It can also hydrolyse ascorbate 2-sulphate (Roy, 1975), monosaccharide sulphates (Roy & Turner, 1982), some steroid sulphates (Waheed & Van Etten, 1980a) and, apparently, adenosine 3',5'-monophosphate (Uchida et al., 1981). The hydrolysis of sulphate esters occurs by fission of the 0-S bond (Spencer, 1958, 1959; Roy & Turner, 1982; Marker & Roy, 1983). Roy (1953a) noted that the extent of the hydrolysis of nitrocatechol sulphate (2-hydroxy-5-nitrophenyl sulphate) by a partially purified sulphatase A from ox liver was not, when measured over I h, linearly related to the enzyme concentration, eo, although it was so related to e0 raised to the power of 3 (Roy, 1953b). It was suggested that this was caused by the polymerization of sulphatase A to a species more catalytically active than the monomer. Dodgson & Spencer (1956), using a similarly purified enzyme from human liver, showed this hypothesis to be untenable and that the 'anomalous' behaviour was caused by the enzyme reaction being not, in general, of zero order. At high enzyme concentrations it approximated to this, but at low concentrations the reaction almost stopped within about 15 min. Roy (1957) subsequently showed the same effects with the ox enzyme. More detailed studies of the human enzyme (Baum & Dodgson, 1958; Baum et al., 1958) showed that the progress curves for the hydrolysis of nitrocatechol sulphate, at pH 5.0 and 37 'C, comprised three stages: stage I, lasting about 15 min, during which the initial velocity rapidly decreased; stage II, a period of very slow hydrolysis; and stage III, during which the reaction velocity increased to a more-or-less constant value which was, however, always less than the initial one. The relative lengths of the stages depended upon the enzyme concentration, as shown in Fig. 1. Baum & Dodgson (1958) concluded that this behaviour was caused by interactions between sulphatase A and its substrate such that during stage I the enzyme was slowly converted to an inactive form which persisted through stage II and was reactivated in stage III by the reaction products (4-nitrocatechol and =0

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@article{Roy1989TheAK, title={The anomalous kinetics of sulphatase A.}, author={Anamitra Bardhan Roy and Timothy J. Mantle}, journal={The Biochemical journal}, year={1989}, volume={261 3}, pages={689-97} }