Galactose Metabolism in Petunia

Dressler, K.; Biedlingmaier, Susanne; Grossberger, H.; Kemmner, J.; Nölle, U.; Rodmanis-Blumer, A.; Heß, Dieter

doi:10.1016/s0044-328x(82)80142-6

Cited by 13 publications

(4 citation statements)

References 36 publications

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“…However, the authors did not identify the reaction products nor did they indicate the magnitude of the measured activity. The report by Dressler et al (1982) on uridyltransferase activity in Petunia is not conclusive since the crude extracts used in this study contained UDP-galactose pyrophosphorylase and UDP-glucose pyrophos- …”

Section: Discussionmentioning

confidence: 55%

“…1). The latter UDP-galactose pyrophosphorylase was reported for higher plant tissues (Maretzki and Thom, 1978;Dressler et al, 1982;Gross and Pharr, 1982), but could not be detected in the primitive acidophilic and thermophilic red alga G. sulphururiu. Instead, in this alga high activity was obtained for galactose 1-phosphate uridyltransferase in the Leloir pathway.…”

Section: Discussionmentioning

confidence: 81%

“…Under these conditions and with UDP-glucose as substrate, UTP could have been generated from UDP-glucose. Therefore, the uridyltransferase activity reported by Dressler et al (1982) was not shown to be UTP independent. This has already been pointed out by Isselbacher (1958) for similar studies on mammalian tissue.…”

Section: Z %mentioning

confidence: 90%

“…Although both the Isselbacher and the Leloir pathway are present in humans, the Leloir pathway is apparently the main route for galactose metabolism (Isselbacher, 1958). In plants, the activity of UDP-galactose pyrophosphorylase has been demonstrated in sugarcane (Maretzki and Thom, 1978) and Petunia (Dressler et al, 1982), and has been well characterized in cucumber (Gross and Pharr, 1982). In contrast, the occurrence of a galactose 1 -phosphate uridyltransferase in plants has still not been demonstrated because this enzyme has never been characterized from plants.…”

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Purification and Characterization of a Galactose‐1‐Phosphate: UDP‐Glucose Uridyltransferase from the Red Alga Galdieria Sulphuraria

Groß

Schnarrenberger

1995

European Journal of Biochemistry

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The galactose-1 -phosphate uridyltransferase of the red alga Galdieria sulphuraria has been purified about 1800-fold to a final specific activity of approximately 140 U/mg protein. The purification involved chromatography on DEAE-Fractogel, hydroxyapatite, decyl-agarose, and DEAE-Tentacle gel. After SDS/ PAGE, the enzyme preparation showed only one protein band of 42 kDa. The enzyme is a homodimer with a molecular mass of 82 kDa as estimated from the sedimentation velocity or 60 kDa as estimated by gel filtration. It has a broad pH optimum between pH 7 and pH 9. The apparent K,,, values for the forward and backward reactions are KJGlclP) = 105 pM, KJUDP-galactose) = 30 pM, KJGallP) = 400 pM, and K,,,(UDP-Glc) = 20 pM. The activation energy of the reaction is 45 kJ mol-I. The enzyme is specific for the galactose 1 -phosphate to UDP-galactose interconversion in the Leloir pathway while the alternate enzyme for the Isselbacher pathway, UDP-galactose pyrophosphorylase, could not be detected in G. sulphuraria.Keywords: galactose-1-phosphate uridlytransferase ; galactose metabolism; Leloir pathway ; Rhodophyta; Galdieria sulphuraria.The sugar galactose is abundant in all organisms. It is generally not found as free galactose but as a constituent of storage products, glycosylation moieties, transport carbohydrates, and especially cell wall material in plants ( Loewus and Tanner, 1982). Free galactose is toxic to most higher plants, and only for Cucumis sativ~is and some algae does galactose treatment lead to a stimulation of growth (Goring and Reckin, 1968). In galactose-sensitive plants, it has been observed that free galactose leads to the accumulation of galactose 1-phosphate and UDP-galactose (Roberts et al., 1971;Inouhe et al., 1987;Loughman et al., 1989). This indicates a limitation in one of the subsequent enzymic reactions. It is supposed that galactose 1-phosphate causes the toxicity because it inhibits the phosphoglucomutase (Roberts et al., 1971) and the UDP-glucose pyrophosphorylase (Yamamoto et al., 1988).The metabolism of galactose has been studied in detail in yeast and mammals, especially in humans because genetic defects in the participating enzymes lead to galactosemia, a severe illness. The pathway of galactose metabolism in plants (Fig. 1) is derived mainly from results obtained for mammalian cells. In the first step of galactose metabolism, the sugar is phosphorylated by a specific galactokinase to yield galactose 1 -phosphate. In the next step, galactose I-phosphate is converted to UDPgalactose. This reaction can be catalyzed either by UDP-galactose pyrophosphorylase, termed the Isselbacher pathway, or by galactose 1 -phosphate uridyltransferase, termed the Leloir pathway. UDP-galactose is then epimerized to UDP-glucose by UDP-galactose 4-epimerase.Although both the Isselbacher and the Leloir pathway are present in humans, the Leloir pathway is apparently the main route for galactose metabolism (Isselbacher, 1958). In plants, the activity of UDP-galactose pyrophosphorylase has been demonstrated in...

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Section: Discussionmentioning

confidence: 55%

Section: Discussionmentioning

confidence: 81%

Section: Z %mentioning

confidence: 90%

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