Dictyostelium discoideum specific activity

Van Dijken, P., Bergsma, J.C., Hiemstra, H.S., De Vries, B., Van Der Kaay, J., and Van Haastert, P.J., 1996, Dictyostelium discoideum contains three inositol monophosphatase activities with different substrate specificities and sensitivities to lithium. Biochem. J. 314 491 195. 

The chemotactic response to cAMP of the slime mould Dictyostelium discoideum is presented as an example. When these cells are starving, they sense cAMP signals, and in response to the hunger signal, cAMP, the cells differentiate (reviewed in ref. 67). In Dictyostelium discoideum the response to cAMP is mediated by G-protein-coupled hepta-helical receptors and is transmitted by the Py subunits of a heterotrimeric G protein. In response to the chemoattractant, cAMP, a homologue of PKB (protein kinase B) is rapidly activated by phosphorylation througji a Ptdins kinase specific for the 3-OH position (see also Chapter 4). 

GDH s of fungal cells are in the soluble phase of the cytosol. In 1963, it was noted that an NAD-GDH of Puccinia helianthi was separated from mitochondria and microsomes by fractional centrifugation (S9). Both NAD- and NADP-GDH s of S. carlsbergensis and S. cerevisiae are cytoplasmic 90,91). Two possible explanations were offered 90). Location outside mitochondria may represent an adaptation to strong repression exerted by glucose on all mitochondrial enzymes in yeast. Alternatively, evolution of a mitochondrial GDH is a late acquisition and coincides with expression of an enzyme that is not specific in its requirements for NAD or NADP. Existence in Dictyostelium discoideum of both a mitochondrial enzyme, which is active with both NAD and NADP, and an extramitochondrial enzyme, which is active only with NAD, tends to support the latter view 4) ... 

Two compounds common in plant metabolism are believed to be precursors of isoprenoid cytokinins in plants adenosine-5 -monophosphate (AMP) and A -isopentenylpyrophos-phate (iPP). As a final product of the mevalonate pathway, the latter substance serves also as a precursor for a wide spectrum of metabolites including some other plant hormones, as abscisic acid, gibberellins and brassinosteroids. The hypothetical scheme of reactions resulting in the formation of iPA, Z and DHZ is given in Fig. 2. The enzyme of entry into isoprenoid cytokinin formation is A -isopentenylpyrophosphate 5 -AMP-A -iso-pentenyltransferase (EC 2.5.1.8, trivially named cytokinin synthetase ). This enzyme activity was first detected in a cell-free preparation from the slime mould Dictyostelium discoideum [7,8]. Later the enzyme from higher plants (cytokinin-independent tobacco callus [9,10] and immature Zea mays kernels [11]) was described and the data were recently summarised in [12], The enzyme is very specific as far as the substrate is concerned [13,14] only the nucleotide AMP can be converted and only iPP (with a double bond in A position) may function as a side chain donor. 

Newell and coworkers found that, during particular stages of fruit construction in Dictyostelium discoideum, four functionally related enzymes accumulated, reached characteristic levels of specific activity, and then disappeared partly or completely. These enzymes were UDP-d-glucose pyrophosphorylase, trehalose 6-phosphate synthetase, UDP-d-galactose 4-epimerase, and UDP-D-galactose polysaccharide n-galactosyl transferase. 

It has been suggested that the evolution of a mitochondrial GDH is a late acquisition, and coincides with the expression of an enzyme which is less specific in its requirements for NAD and NADP (Smith et ai, 1975). This view is supported by the fact that plant and animal mitochondrial enzymes show less specificity toward coenzymes than do the cytoplasmic enzymes of the fungi. Dictyostelium discoideum possesses a mitochondrial enzyme with dual coenzyme specificity, and a cytoplasmic enzyme active with only NAD", supporting the above hypothesis (De Toma and Langridge, 1974). 

Nucieotidases.—Since the 5 -nucleotidase from Dictyostelium discoideum interacted with immobilized concanavalin A, it appears to be a glycoprotein. Pectinesterases.—The occurrence, formation, assay, purification, and specificities of pectinesterases have been reviewed. Pectinesterase activity was detected both in healthy and diseased onions Allium cepa), but not in cultures of the invading bacterium (Pseudomonas cepacia) Both the pectinesterase and poly-D-galact-uronate lyase activities of Clostridium multifermentans are associated with a single complex. ... 

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