The green alga Scenedesmus obliquus contains both diadenosine 5′,5‴-P1,P4-tetraphosphate (asymmetrical) pyrophosphohydrolase and phosphorylase activities

Abstract

Diadenosine 5',5'''-P1,P4-tetraphosphate (Ap4A) phosphorylase and Ap4A pyrophosphohydrolase activities have been purified from extracts of the green alga Scenedesmus obliquus. Both activities were also detected in Scenedesmus brasiliensis, Scenedesmus quadricauda and in Chlorella vulgaris. This is the first time that both types of enzyme have been detected in the same species. The Ap4A phosphorylase has a molecular mass of 46-48 kDa, a broad pH optimum between 7.5 and 9.5, and requires a divalent ion for activity (Mg2+ > Co2+ > Ca2+ = Mn2+ = Cd2+ > Zn2+). It degrades substrates with at least four phosphate groups and always produces a nucleoside 5'-diphosphate product. The Km values for Ap4A and Pi are 5.3 microM and 160 microM, respectively, and kcat. = 1.8 s-1. Arsenate, vanadate, molybdate, chromate and tungstate can substitute for phosphate. The enzyme also catalyses Ap4A synthesis (Keq. = [Ap4A] [Pi]/[ATP][ADP] = 9 x 10(-4)) and ADP arsenolysis. The Ap4A hydrolase has a molecular mass of 26-28 kDa, an alkaline pH optimum of 8.8-9.8, and prefers Zn2+ as the stimulatory ion (Zn2+ > Mg2+ > Mn2+ > Co2+ > Cd2+). It degrades substrates with at least four phosphate groups, having a slight preference for Ap5A, and always produces a nucleoside 5'-triphosphate product. The Km value for Ap4A is 6.6 microM and kcat. = 1.3 s-1. It is inhibited competitively by adenosine 5'-tetraphosphate (Ki = 0.67 microM) and non-competitively by fluoride (Ki = 150 microM). A 50-54 kDa dinucleoside 5',5'''-P1,P3-triphosphate (Ap3A) pyrophosphohydrolase was also detected in S. obliquus, S. quadricauda and C. vulgaris. The corresponding enzyme in S. brasiliensis (> 100 kDa) may be a dimer

The Saccharomyces cerevisiae YOR163w Gene Encodes a Diadenosine 5′,5‴-P 1,P 6-Hexaphosphate (Ap6A) Hydrolase Member of the MutT Motif (Nudix Hydrolase) Family

“…Thus, there may be a closer evolutionary relationship between the plant and fungal Ap n A hydrolases. Another activity that may be related is the dinucleoside polyphosphate hydrolase purified from the green alga Scenedesmus obliquus, an organism that, like S. cerevisiae, has an Ap 4 A phosphorylase (34). This enzyme hydrolyzes Ap n A with the preference Ap 5 A Ͼ Ap 4 A Ͼ Ap 6 A.…”

“…Given the current power of genetic manipulation in yeast, phenotypic analysis of YOR163w knockouts in appropriate genetic backgrounds (e.g. apa1 and apa2 mutants) should help determine the role(s) of this enzyme and the relative contribution of hydrolases and phosphorylases to Ap n A catabolism and function in those organisms in which both types of enzyme exist (34).…”

Fhit proteins can also recognize substrates other than dinucleoside polyphosphates

“…This enzyme was first discovered in SillerosÕ laboratory in extracts of rat liver [8] and subsequently in extracts of yellow Abbreviations: APS or S-pA, adenosine 5 0 -phosphosulfate; NH 2 -pA, adenosine 5 0 -phosphoramidate; ATP-F or F-pppA, adenosine 5 0 -O-(c-fluorotriphosphate); HPLC, high performance liquid chromatography; TLC, thin layer chromatography lupin seeds [9], Saccharomyces cerevisiae [10], Artemia [11], and green algae [12]. The intriguing finding that FHIT (from fragile histidine triad), a putative human tumor suppressor gene, encodes a typical dinucleoside triphosphatase [13] focused much attention on this particular enzyme.…”

Human diadenosine 5′,5′′′-P1,P4-tetraphosphate pyrophosphohydrolase is a member of the MutT family of nucleotide pyrophosphatases

“…Curiously, certain green algae, e.g. Scenedesmus obliquus, have an asymmetrical Ap4A hydrolase in addition to Ap4A phosphorylase [16].…”