Previous results (Pasternak, Kent & Davies, 1958) showed that 35SO42ion is utilized in differing degrees by surviving intestinal tissues and that the ion is incorporated as sulphate esters of intestinal mucins (Pasternak & Kent, 1958). The incorporation is energy-dependent and inhibitors of respiration also prevent the uptake of sulphate. A relatively high level of incorporation of SO42ion was found in colonic mucosa, and on account of its availability and ease of homogenization this tissue was selected for an investigation of the individual stages of the sulphation mechanism. In liver, formation of phenolic sulphates involves the enzymic activation of SO42ions by combination with adenosine triphosphate (ATP), forming adenosine 3'-phosphate 5'-phosphosulphate (Hilz & Lipmann, 1955). D'Abramo & Lipmann (1957) secured, from chick-embryo condyles, cell-free preparationm which promote the incorporation of 35SO42ion into chondroitin sulphate, with indications that a similar sulphate-activation mechanism participates. MATERIALS AND METHODS Preparation of tissue homogenates. A portion of the large intestine (approx. 30 cm. from the anus) of adult sheep was obtained immediately after slaughter and placed in icecold saline. Within 30 min. the intestine was emptied, rinsed with water and transferred to ice-cold KCI solution (0-9 %) brought to pH 7-5 with a little 2-amino-2-hydroxymethylpropane-1:3-diol (tris). The mucosa (12-5 g.), removed by scraping with a scalpel, was immersed in 25 ml. of 0-25M-sucrose or KCI (0-9%) at 0°, eagh solution being brought to pH 8-5 by addition of tris. The tissue was then homogenized (12 strokes) in a chilled Potter-type stainlesssteel apparatus. Fractionation of homogenates. The homogenate (37 ml.) was centrifuged at 00 for 20 min. at 24 000g. The clear supernatant fraction (22 ml.) was decanted and used in the experiments described below. The precipitate was resuspended in 12 ml. of 0-25M-sucrose before investigation. Incubations. Experiments (Table 1) were performed under 02 in Warburg manometer flasks at 370 for 30-60 min., the centre well containing NaOH on filter paper. Each flask contained 0-1 m-sodium phosphate buffer (pH 7-6, 0-4 ml.), 0-2ar-MgCl2 (0-2 ml.), 0-154m-MgSO4 (0-036 ml.), 0-O2M-ATP (0-2 ml.), 10juc of Na,,35SO4 (approx. 0-1 ml.) and 0-2 ml. of a solution containing 0-5Msodium pyruvate and 0-04M-sodium fumarate. In each case 3 ml. of a suspension of mucosal scrapings or other enzyme fraction was added. In appropriate cases, 0-5msodium fluoride (0-3 ml.