Cytidine monophosphate-N-acetylneuraminate hydroxylase in the starfish Asterias rubens and other echinoderms.
The sialic acid N-glycolylneuraminic acid (Neu5Gc) is synthesised by an NADH-dependent hydroxylase which acts on CMP-N-acetylneuraminic acid (CMP-Neu5Ac). Although Neu5Gc is the predominant sialic acid in many echinoderms, little is known about the hydroxylase from organisms of this phylum. We show here that in contrast to the mammalian enzyme, the hydroxylase from various echinoderms is predominantly membrane-bound and exhibits optimal activity in the presence of 100 mM NaCl. A detailed characterisation of the hydroxylase from echinoderms was performed using fractionated gonads of the starfish Asterias rubens. Solubilisation using detergents led to an inactivation of the hydroxylase. However, the solubilised enzyme was reactivated by the addition of cytochrome b5 reductase together with the amphiphilic or soluble form of cytochrome b5. Although these latter proteins were only available from a mammalian source, the high affinity of the hydroxylase for cytochrome b5 suggests that, as with the mammalian enzyme, these electron carriers participate in the catalytic cycle of the hydroxylase from A. rubens in vivo. The relevance of these results to the interaction between cytochrome b5 and the hydroxylase is discussed.
Gollub
M
M
Biochemisches Institut der Christian-Albrechts-Universität zu Kiel, Germany.
Schauer
R
R
Shaw
L
L
D000818:Animals; D003579:Cytochrome Reductases / Q000378:metabolism; D042966:Cytochrome-B(5) Reductase; D015786:Cytochromes b5 / Q000378:metabolism; D004447:Echinodermata / Q000201:enzymology*; D004579:Electron Transport; D006066:Gonads / Q000201:enzymology; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008862:Microsomes, Liver / Q000378:metabolism; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D009994:Osmolar Concentration; D012616:Sea Cucumbers / Q000201:enzymology; D012617:Sea Urchins / Q000201:enzymology; D012995:Solubility; D013045:Species Specificity; D013215:Starfish / Q000201:enzymology*; D013347:Subcellular Fractions / Q000201:enzymology; D013552:Swine; D013696:Temperature
D015786:Cytochromes b5; D006899:Mixed Function Oxygenases; C074383:CMPacetylneuraminate monooxygenase; D003579:Cytochrome Reductases; D042966:Cytochrome-B(5) Reductase