Glucose-induced inactivation of isocitrate lyase in is mediated by the cAMP-dependent protein kinase catalytic subunits Tpk 1 and Tpk2

Departamento de Bioquimica y Biologia Molecular e Instituto Universitario de Biotecnologia de Asturias (IUBA), Universidad de Oviedo, 33006 Oviedo, Spain
FEBS Letters (Impact Factor: 3.17). 04/1996; 385(1-2):43-46. DOI: 10.1016/0014-5793(96)00344-4


Glucose-induced inactivation of isocitrate lyase (Icl) has been related to protein phosphorylation. Moreover, since rapid reversible inactivation preceded irreversible inactivation of the enzyme, phosphorylation was proposed as the triggering reaction that makes the enzyme accessible to the proteolytic machinery. The protein kinase involved in the process is unknown at the moment. In this work we demonstrate that Tpk1 and Tpk2, the catalytic subunits of cAMP-dependent protein kinase, are involved in the signalling of short-term and long-term inactivation processes of Icl. We also demonstrate that threonine 53 is involved in a regulatory mechanism necessary for short-term reversible inactivation of Icl, probably mediated through its phosphorylation. Other, as yet unidentified, residues are likely to be the target of distinct protein kinases mediating the irreversible long-term inactivation of Icl.

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    • "However, this activity was much lower than the activity achieved during growth on mixture of ethanol and d-glycerol. This observation - in addition to the role of glucose repression [18,33] - is possibly explained by glucose-induced post-translational modifications such as phosphorylation [34,35] or proteolytic inactivation [36], which have been shown to regulate Icl1p activity. "
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    • "This is consistent with the observation that phosphorylation of FbPase by PKA is strongly activated by fructose-2,6-bispho- sphate, a regulatory metabolite that is formed when glucose is metabolized (Gancedo et al., 1983). While partial inactivation of isocitrate lyase by glucose is also dependent on phosphorylation by PKA (Ordiz et al., 1996), there is no information on the protein kinase(s) performing the phosphorylation of the malate dehydrogenase isoenzyme Mdh2 "
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    • "A similar site has been found in C. cinereus acu7 (Chaure et al., 1997), and ICL1 sequences of S. cerevisiae (Fernández et al., 1992) and Candida tropicalis (Atomi et al., 1990). In particular, S. cerevisiae ICL1 has been proposed to be phosphorylated at T53, followed by inactivation in the presence of glucose (Ló pez-Boado et al., 1988; Ordiz et al., 1996). However, the role of the motif KRGT in FPICL1 remains to be assessed. "
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    ABSTRACT: This study investigated the subcellular localization of key enzymes of the glyoxylate cycle, i.e. isocitrate lyase (ICL; EC and malate synthase (EC, that function constitutively in coordination with oxalate biosynthesis of glucose-grown Fomitopsis palustris. The ICL purified previously from F. palustris is termed FPICL1. Subcellular fractionation analysis of the cell homogenate by the sucrose density-gradient method showed that both key enzymes were present in peroxisomes, whereas acetyl-CoA synthase (EC and oxalate-producing oxaloacetate acetylhydrolase (EC were cytosolic. The peroxisomal localization of FPICL1 was further confirmed by electron microscopic and immunocytochemical analysis with anti-FPICL1 antibody. In addition, the peroxisomal target signal, composed of SKL at the C terminus of the cDNA encoding FPICL1, was found, which also suggests that FPICL1 is peroxisomal. Accordingly, it is postulated that transportation of succinate from peroxisomes to mitochondria, and vice versa, for the transportation of isocitrate or citrate, occurs in glucose-grown F. palustris for the constitutive metabolic coordination of the TCA and glyoxylate cycles with oxalate biosynthesis.
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