Kemptide is a synthetic heptapeptide that acts as a substrate for cAMP-dependent protein kinase (PK) [1].

Cyclic AMP-dependent protein kinase is the sole intracellular acceptor for cyclic AMP in all cell types. Protein phosphorylation by different types of protein kinase (PK) activities comprises a form of protein modification that plays an important role in the regulation of numerous biological processes [1][2].

Kemptide is a novel synthetic heptapeptide phosphate acceptor that acts as a substrate for cAMP-dependent protein kinase. Kemptide had all the properties of a cytophilic substrate and could preserving cell membrane intactness when added to cultured cells. In the presence of extracellular ATP and cAMP, different types of intact cells catalyzed the phosphorylation of Kemptide with Km values of 3-4 μM. Kemptide phosphorylation was influenced by PKI, the inhibitory protein specific for cAMP-PK [1]. Kemptide was usually used as a substrate for detection of activities of soluble A-kinase isolated from guinea-pig lung parenchyma and from bovine tracheal smooth muscle [2][3].

References:
[1].  Kübler D, Pyerin W, Bill O, et al. Evidence for ecto-protein kinase activity that phosphorylates Kemptide in a cyclic AMP-dependent mode. J Biol Chem. 1989 Aug 25;264(24):14549-55.
[2].  Giembycz MA, Diamond J. Evaluation of kemptide, a synthetic serine-containing heptapeptide, as a phosphate acceptor for the estimation of cyclic AMP-dependent protein kinase activity in respiratory tissues. Biochem Pharmacol. 1990 Jan 15;39(2):271-83.
[3].  Langlands JM, Rodger IW. Determination of soluble cAMP-dependent protein kinase activity in guinea-pig tracheal smooth muscle. Preferential use of kemptide as a phosphorylating substrate. Biochem Pharmacol. 1990 Apr 15;39(8):1365-74.