Characterization of sulphotransferase in human ileum and colon

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 less than 0.01). Vmax for the low-affinity phase was 669 +/- 105 (ileum) and 415 +/- 84 (colon) (p less than 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 less than 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.