In Dictyostelium discoideum inositol 1,3,4,5-tetrakisphosphate is dephosphorylated by a 3-phosphatase and a 1-phosphatase.
The degradation of Ins(1,3,4,5)P4 in Dictyostelium was investigated using a mixture of [3H]Ins(1,3,4,5)P4 and [3-32P]Ins-(1,3,4,5)P4. After incubation of this mixture with a Dictyostelium homogenate the 32P/3H ratio found in the InsP3 product was reduced to 24% of the ratio in the substrate. 32P-labelled inorganic phosphate was found as well, whereas hardly any InsP2 was detected. This indicates that Ins(1,3,4,5)P4 is mainly degraded by a 3-phosphatase. The other enzyme was characterized by identification of the 32P-labelled InsP3 isomer. This isomer did not co-elute with Ins(1,3,4)P3, indicating that no 5-phosphatase was present in Dictyostelium. The 32P-labelled InsP3 could be oxidized using NaIO4. The only InsP3 isomer that has these characteristics is Ins(3,4,5)P3, indicating 1-phosphatase activity. The 1-phosphatase appeared to be dependent on MgCl2, whereas the 3-phosphatase was still active in the absence of MgCl2. An analogue of Ins(1,3,4,5)P4 with a thiophosphate substitution at the 1-position was found to be almost completely resistant to hydrolysis by the 1-phosphatase, but was degraded by the 3-phosphatase.
Van Dijken
P
P
Department of Biochemistry, University of Groningen, The Netherlands.
Lammers
A A
AA
Van Haastert
P J
PJ
D000818:Animals; D004023:Dictyostelium / Q000378:metabolism*; D004492:Edetic Acid / Q000494:pharmacology; D007295:Inositol Phosphates / Q000378:metabolism*; D010504:Periodic Acid / Q000737:chemistry; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*
D007295:Inositol Phosphates; C081655:inositol-1,3,4,5-tetrakisphosphate; D010504:Periodic Acid; D004492:Edetic Acid; C009288:metaperiodate; D010744:Phosphoric Monoester Hydrolases; C064119:multiple inositol-polyphosphate phosphatase