l-Tryptophan, but not d-tryptophan, inhibits human placental and intestinal alkaline phosphatases, but not those of liver and bone. The nature of this stereospecific organ-specific inhibition has been elucidated. Thus, from a study of the effect of substrate concentration on inhibition in which double-reciprocal plots of 1/v versus 1/s at various inhibitor concentrations were made, this inhibition is judged to be ‘uncompetitive’. That the inhibition is non-allosteric is an opinion based on (1) hyperbolic curves obtained from plotting the percentage inhibition against inhibitor concentration; (2) the independence of the inhibition to heat denaturation and urea treatment; (3) the relatively low value of entropy change; and (4) a value close to unity for n, the number of l-tryptophan molecules that combine with one molecule of enzyme. Finally, a homosteric mechanism is further postulated for the inhibition by l-tryptophan based on the increase of optimum temperature for maximum velocity and the decrease of this inhibition with increasing temperature. The mechanism of this inhibition is discussed.
Research Article|September 01 1971
l-Tryptophan. A non-allosteric organspecific uncompetitive inhibitor of human placental alkaline phosphatase
C W Lin;
H G Sie;
Biochem J (1971) 124 (3): 509-516.
- Views Icon Views
- PDF LinkPDF
- Share Icon Share
- Cite Icon Cite
C W Lin, H G Sie, W H. Fishman; l-Tryptophan. A non-allosteric organspecific uncompetitive inhibitor of human placental alkaline phosphatase. Biochem J 1 September 1971; 124 (3): 509–516. doi: https://doi.org/10.1042/bj1240509
Download citation file: