Characterization of Sulphotransferase in Human Ileum and Colon

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Abstract
The kinetics of sulphotransferase (ST) were studied at varying concentrations of 2-naphthol or adenosine 3’-phosphate-5’-phosphosulphate (PAPS) in specimens of ileum and colon mucosa obtained from 6 subjects. When 2-naphthol was the variable substrate the enzyme obeyed non-Michaelis-Menten kinetics. The enzyme kinetic profile consists of two phases: one at higher and the other at lower activity for 2-naphthol. The maximum velocity of reaction (Vmax, mean ± SD; pmol/min·mg protein) of the high-affinity phase was 403 ± 82 (ileum) and 216 ± 42 (colon) (p < 0.01). Vmax for the low-affinity phase was 669 ± 105 (ileum) and 415 ± 84 (colon) (p < 0.01). Km (mean ± SD) of the high affinity phase was 0.034 ± 0.004 (ileum) and 0.025 ± 0.001 mmol/l (colon) (NS) and that of the low-affinity phase was 0.101 ± 0.013 (ileum) and 0.095 ± 0.014 mmol/l (colon) (NS). At varying concentrations of PAPS the enzyme obeyed Michaelis-Menten kinetics. Vmax (mean ± SD) was 995 ± 163 (ileum) and 520 ± 114 (colon) pmol/min·mg protein (p < 0.02). Km was 0.096 ± 0.008 (ileum) and 0.079 ± 0.012 mmol/l (colon) (NS). The ST of ileum differs from that of colon for Vmax only.

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