Alkaline phosphatases (AP), act as non-specific phosphomonoesterases to hydrolyse phosphate esters, optimally at high pH. Garbers, et al>., show that alkaline phosphatases preferentially dephosphorylate proteins containing phosphotyrosine. The so-called alkaline phosphatases, then, may be a group of membrane-bound glycoproteins that represent a class of phosphoprotein phosphatases that show selectivity for proteins phosphorylated at tyrosine residues (1). In addition, recent studies have demonstrated that ecombinant gIAP can dephosphorylate CD36 at a threonine residue (2).

Reference
1. Swarup G, Cohen S and Garbers DL. (1981) Selective dephosphorylation of proteins containing phosphotyrosine by alkaline phosphatases. J Biol Chem, 256, 8197-201. PMID: 6167574
2. Lynes M, Narisawa S, Millán JL and Widmaier EP. (2011) Interactions between CD36 and global intestinal alkaline phosphatase in mouse small intestine and effects of high-fat diet. Am J Physiol Regul Integr Comp Physiol, 301, R1738-47. PMID: 21900644

    SSU72 was originally identified as a transcription/RNA processing factor interacting with the TFIIB transcription factor in yeast. Further studies show that SSU72 can also mediate the regulation of cell viability and it is conserved among eukaryotic organisms. SSU72 possesses the phosphatase activity and the conserved catalytic motif CX5R of PTP also presents in SSU72. SSU72 is thought to be Asp-based PTP and the mutation of aspartate will lead to the decreased phosphatase activity. One identified substrate is C-terminal domain of RNA polymerase II (1).

Reference
1. Kim, H.S., Baek, K.H., Ha, G.H., Lee, J.C., Kim, Y.N., Lee, J., Park, H.Y., Lee, N.R., Lee, H., Cho, Y. et al. (2010) The hsSsu72 phosphatase is a cohesin-binding protein that regulates the resolution of sister chromatid arm cohesion. EMBO J, 29, 3544-3557. PMID: 20818333