Two dephosphorylation pathways of inositol 1,4,5-trisphosphate in homogenates of the cellular slime mould Dictyostelium discoideum

Abstract

Dictyostelium discoideum homogenates contain phosphatase activity which rapidly dephosphorylates Ins(1,4,5)P3 (D-myo-inositol 1,4,5-trisphosphate) to Ins (myo-inositol). When assayed in Mg2", Ins(1,4,5)P3 is dephosphorylated by the soluble Dictyostelium cell fraction to 20% Ins(1,4)P2 (D-myo-inositol 1,4-bisphosphate) and 80 % Ins(4,5)P2 (D-myo-inositol 4,5-bisphosphate). In the particulate fraction Ins(1,4,5)P, 5-phosphatase is relatively more active than the Ins(1,4,5)P3 1-phosphatase. CaCl2 can replace MgCl2 only for the Ins(1,4,5)P3 5-phosphatase activity. Ins(1,4)P2 and Ins(4,5)P2 are both further dephosphorylated to Ins4P (D-myo-inositol 4-monophosphate), and ultimately to Ins. Li' ions inhibit Ins(1,4,5)P3 l-phosphatase, Ins(1,4)P2 1 -phosphatase, Ins4P phosphatase and L-Ins1 P (L-myo-inositol 1 -monophosphate) phosphatase activities; Ins(1,4,5)P3 I-phosphatase is 10-fold more sensitive to Li' (half-maximal inhibition at about 0.25 mM) than are the other phosphatases (half-maximal inhibition at about 2.5 mM). Ins(1,4,5)P3 5-phosphatase activity is potently inhibited by 2,3-bisphosphoglycerate (half-maximal inhibition at 3 /tM).Furthermore, 2,3-bisphosphoglycerate also inhibits dephosphorylation of Ins(4,5)P2. These characteristics point to a number of similarities between Dictyostelium phospho-inositol phosphatases and those from higher organisms. The presence of an hitherto undescribed Ins(1,4,5)P3 1-phosphatase, however, causes the formation of a different inositol bisphosphatase isomer [Ins(4,5)P2] from that found in higher organisms [Ins(1,4)P2]. The high sensitivity of some of these phosphatases for Li' suggests that they may be the targets for Li' during the alteration of cell pattern by Li' in Dictyostelium.

Sensory transduction in eukaryotes

“…The similarities and differences of the metabolism of Ins (1,4,5 [269]. The presence of multiple dephosphorylation routes in D. discoideum suggests that these routes are regulated and that the InsP2 products may have specific functions.…”

Soluble and particulate Ins(1,4,5)P3/Ins(1,3,4,5)P4 5‐phosphatase in bovine brain

“…The ratio of the 32P label recovered with respect to the 3H label in the InsP2 column fraction was determined. As the I n~ ( 1 , 4 , 5 ) [~~P ] P~ was labeled in the 5 position, a low 32P/3H ratio in the InsP, fraction indicates essentially 5-phosphatase activity, whereas a high ratio in the InsP, fraction indicates 1 and/or 4-phosphatase activity [17]. 32P/3H ratios in the InsP2 fraction were 10 -16% of the original ratio in the Ins(1 ,4,5)P3 substrate suggesting 5-phosphatase activity.…”

Metabolism of Inositol(1,4,5)trisphosphate by a Soluble Enzyme Fraction from Pea (Pisum sativum) Roots

“…In mammalian cells the removal of Ins( 1 ,4,5)P3 from the cytosol is generally found to be undertaken by a 5-phosphohydrolase and a 3-hydroxykinase, Ins(1,4)P2 and Ins(1,3,4,5)P4 being the resulting products. However, in studies using homogenates from the slime mould Dictyostelium discoideum, Van Lookeren Campagne et al (29) found that Ins(1,4,5)P3 was rapidly dephosphorylated to 20% Ins(1,4)P2 and 80% Ins(4,5)P2, followed by further dephosphorylation of Ins(4,5)P2 and Ins(1,4)P2 to Ins(4)P and inositol. These findings, when seen in conjunction with the data presented above (see Fig.…”

“…As shown in Figure 7, 10 mm of selected phosphohydrolase substrates partially inhibited the 1-phosphohydrolase activity by approximately 55% during 5 min incubations. Van Lookeren Campagne et al (29) found that the Ins(1,4,5)P3-1-phosphohydrolase ofDictyostelium was inhibited biphasically by 2,3-DPG with a reduction in hydrolysis to less than 10% of control by 10 mM 2,3-DPG. Our data show that the Ins( 1,4,5)P3-I-phosphohydrolase activity in pea roots is considerably less sensitive to 2,3-DPG than the corresponding activity in Dictyostelium.…”