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. Author manuscript; available in PMC: 2014 Mar 24.
Published in final edited form as: Biochem J. 2011 Mar 15;434(3):415–426. doi: 10.1042/BJ20101437

Table 1. Kinetic constants for PPIP5K1 catalytic domain.

The kcat/Km ratios (specificity constants) were determined from the enzyme concentration and first-order rate constants for the metabolic reactions described in Figure 1, except for Ins(1,3,4,5,6)P5 phosphorylation. The data for intracellular concentrations were taken from various sources. Several publications have put the cellular concentration of PP-InsP5 in the 1–5 μM range (see [4] for a summary); a mid-range value of 2 μM is given in this Table. The values for the concentrations of Ins(1,3,4,5,6)P5 and InsP6 [48] are at the high end of a range of estimates [49]. MDD–HPLC analysis indicates that 1/3-PP-InsP5 must be <10 % of the cellular concentration of 5-PP-InsP5 [5,11].

Substrate Concentration in vivo (M) kcat/Km (104×M−1 s−1) [S]×kcat/Km (s −1)
5-PP-InsP5 2 × 10 −6 384 ± 10 7.7
InsP6 40 × 10 −6 4.8 ± 0.3 1.9
Ins(1,3,4,5,6)P5 90 × 10 −6 0.3 ± 0.01 0.021
1/3-PP-InsP5 0.2 × 10 −6 0.11 ± 0.04 0.0002