The Michaelis-Menten equation was fitted to simulated data containing different sorts of error by using the three linear transformations, and the methods of S. R. Cohen [Anal. Biochem. (1968) 22, 549-552], R. Eisenthal & A. Cornish-Bowden [Biochem. J. (1974) 139, 715-120], F. de M. Merino [Biochem. J. 143, 93-95] and G. N. Wilkinson [Biochem. J. (1961) 808 324-332). The best methods were those of Eisenthal & Cornish-Bowden (1974) and Wilkinson (1961).

1. Experimental progress curves were simulated for a reaction obeying Michaelis-Menten kinetics. 2. K(m) and V were estimated (a) by fitting the integrated Michaelis-Menten equation to the progress curves, and (b) from the initial slopes of the curves (i.e. from initial velocities). 3. The integrated equation could not be fitted successfully by a non-linear method, so it was transformed and fitted by a linear method. 4. Provided that the initial substrate concentration was greater than K(m) and the data were precise enough, the integrated equation gave parameter estimates which were unbiased and as reliable as those derived from initial velocities although based on fewer experiments. 5. The integrated equation could be used for progress curves of unknown origin.

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Substantial soluble glutathione S-transferase activity and millimolar reduced glutathione (GSH) are present in most tissues of both teleosts and elasmobranchs. The hepatic enzymes of fish conjugate a range of electrophilic substrates with GSH, although their specificities are less broad than those of the transferases in rodent liver. There is no good evidence that fish transferases have ligandin-like activity or a 'suicide' function. All fish livers tested have several transferase isoenzymes. They are dimers of subunits whose Mrs are about 25 kDa and which may have different catalytic properties. In some species transferase activity is induced by agents such as phenols or 3-methylcholanthrene. Glutathione S-transferases are important detoxication enzymes in fish.