| Abstract | A paper published in 2005 by Saini et al. put forward the use of L-phe-gly-gly, known to be an allosteric inhibitor of placental alkaline phosphatase (PLAP), along with pNPP in PBS, pH 8.0 to purify PLAP from the protein extract. This is an interesting and insightful approach for purification especially since it enables specific targeting of an enzyme or even a specific isozyme through effectors termed as activity based probes or ABPs. The aim of this study is to identify the characteristics of inhibition using the same conditions as the 2005 paper but with another effector - L-leu - which uncompetitively inhibits PLAP in order to determine if this could be an alternative option for purification. Accordingly, it was hypothesized that L-leu will uncompetively inhibit PLAP and this would be characreized by the change in Vmax and Km. This was done through an enzyme assay utilizing pNPP which is hydrolysed by PLAP to produce a yellow product (NPP). This product absorbs at 410nm and can give a direct readout of the enzyme reaction rate per minute using a UV spectrophotometer. A decrease in Vmax and Km was observed when the inhibitor was present versus when it was not. This means that the activity of the enzyme could not effectively catalyse as many substrate when the inhibitor was present and needed less substrate to bind to the enzyme to reach 1/2 of Vmax.
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