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. 1971 Sep;124(3):509–516. doi: 10.1042/bj1240509

l-Tryptophan. A non-allosteric organspecific uncompetitive inhibitor of human placental alkaline phosphatase

Chi-Wei Lin 1, Hsein-Gieh Sie 1, William H Fishman 1
PMCID: PMC1177219  PMID: 5135237

Abstract

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.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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