Structure-activity studies of sulfate transfer: the hydrolysis and aminolysis of 3'-phosphoadenosine 5'-phosphosulfate (PAPS).
The pH-rate profile for the hydrolysis of 3'-phosphoadenosine 5'-phosphosulfate (PAPS) in aqueous solution has been measured. Comparison with other data suggests that hydrolysis occurs by almost complete unimolecular elimination of sulfur trioxide, with weak involvement of a molecule of water in the transition state. The catalytic power (kcat/kuncat) of the sulfotransferases is estimated to be in the order of 10(10)-10(12). Amines--exemplified by morpholine--react spontaneously with PAPS in water at 39 degrees C by attack at both sulfuryl and (5')phosphoryl groups in a ratio of 2:3. The mechanism of activation of the coenzyme, PAPS, by the sulfotransferases that catalyse N-sulfation must involve suppression of its native N-phosphorylating reactivity and specific enhancement of its N-sulfating reactivity. Studies of the aminolysis of the coenzyme in aprotic solvent-water mixtures suggest how this might be accomplished.
Bedford
C T
CT
School of Biological & Health Sciences, University of Westminster, London, U.K.
Kirby
A J
AJ
Logan
C J
CJ
Drummond
J N
JN
D000588:Amines / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D004121:Dimethyl Sulfoxide; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D009025:Morpholines / Q000737:chemistry; D009994:Osmolar Concentration; D010724:Phosphoadenosine Phosphosulfate / Q000737:chemistry*; D010879:Piperazines / Q000737:chemistry; D013329:Structure-Activity Relationship; D013431:Sulfates / Q000737:chemistry*
D000588:Amines; D009025:Morpholines; D010879:Piperazines; D013431:Sulfates; D010724:Phosphoadenosine Phosphosulfate; C037574:morpholine; C007306:triethylenediamine; D004121:Dimethyl Sulfoxide