EC 1.1.1.249      
Deleted entry: Provisional entry deleted. Revised and reinstated as EC 2.5.1.46 deoxyhypusine synthase
[EC 1.1.1.249 provisional version created 1999, deleted 1999 (reinstated 2001 as EC 2.5.1.46)]
 
 
EC 1.14.99.29     
Accepted name: deoxyhypusine monooxygenase
Reaction: [eIF5A]-deoxyhypusine + reduced acceptor + O2 = [eIF5A]-hypusine + acceptor + H2O
Glossary: deoxyhypusine = N6-(4-aminobutyl)-L-lysine
hypusine = N6-[(R)-4-amino-2-hydroxybutyl]-L-lysine
Other name(s): deoxyhypusine hydroxylase; deoxyhypusine dioxygenase
Systematic name: deoxyhypusine,hydrogen-donor:oxygen oxidoreductase (2-hydroxylating)
Comments: The enzyme catalyses the final step in the formation of the amino acid hypusine in the eukaryotic initiation factor 5A.
References:
1.  Abbruzzese, A., Park, M.H. and Folk, J.E. Deoxyhypusine hydroxylase from rat testis. Partial purification and characterization. J. Biol. Chem. 261 (1986) 3085–3089. [PMID: 3949761]
[EC 1.14.99.29 created 1989]
 
 
EC 2.5.1.44     
Accepted name: homospermidine synthase
Reaction: (1) 2 putrescine = sym-homospermidine + NH3 + H+
(2) putrescine + spermidine = sym-homospermidine + propane-1,3-diamine
Glossary: sym-homospermidine = N-(4-aminobutyl)butane-1,4-diamine
putrescine = butane-1,4-diamine
dehydroputrescine = 4-iminobutan-1-amine
Systematic name: putrescine:putrescine 4-aminobutyltransferase (ammonia-forming)
Comments: The reaction of this enzyme occurs in three steps, with some of the intermediates presumably remaining enzyme-bound: NAD+-dependent dehydrogenation of putrescine, transfer of the 4-aminobutylidene group from dehydroputrescine to a second molecule of putrescine and reduction of the imine intermediate to form homospermidine. Hence the overall reaction is transfer of a 4-aminobutyl group. Differs from EC 2.5.1.45, homospermidine synthase (spermidine-specific), which cannot use putrescine as donor of the aminobutyl group.
References:
1.  Tait, G.H. The formation of homospermidine by an enzyme from Rhodopseudomonas viridis. Biochem. Soc. Trans. 7 (1979) 199–200. [PMID: 437275]
2.  Böttcher, F., Ober, D. and Hartmann, T. Biosynthesis of pyrrolizidine alkaloids: putrescine and spermidine are essential substrates of enzymatic homospermidine formation. Can. J. Chem. 72 (1994) 80–85.
3.  Yamamoto, S., Nagata, S. and Kusaba, K. Purification and characterization of homospermidine synthase in Acinetobacter tartarogens ATCC 31105. J. Biochem. 114 (1993) 45–49. [PMID: 8407874]
4.  Srivenugopal, K.S. and Adiga, P.R. Enzymatic synthesis of sym-homospermidine in Lathyrus sativus T (grass pea) seedlings. Biochem. J. 190 (1980) 461–464. [PMID: 7470060]
5.  Ober, D., Tholl, D., Martin, W. and Hartmann, T. Homospermidine synthase of Rhodopseudomonas viridis: Substrate specificity and effects of the heterologously expressed enzyme on polyamine metabolism of Escherichia coli. J. Gen. Appl. Microbiol. 42 (1996) 411–419.
6.  Ober, D. and Hartmann, T. Homospermidine synthase, the first pathway-specific enzyme of pyrrolizidine alkaloid biosynthesis, evolved from deoxyhypusine synthase. Proc. Natl. Acad. Sci. USA 96 (1999) 14777–14782. [PMID: 10611289]
[EC 2.5.1.44 created 1999, modified 2001]
 
 
EC 2.5.1.45     
Accepted name: homospermidine synthase (spermidine-specific)
Reaction: spermidine + putrescine = sym-homospermidine + propane-1,3-diamine
Glossary: sym-homospermidine = N-(4-aminobutyl)butane-1,4-diamine
putrescine = butane-1,4-diamine
spermidine = N-(3-aminopropyl)butane-1,4-diamine
Systematic name: spermidine:putrescine 4-aminobutyltransferase (propane-1,3-diamine-forming)
Comments: The reaction of this enzyme occurs in three steps, with some of the intermediates presumably remaining enzyme-bound: (a) NAD+-dependent dehydrogenation of spermidine, (b) transfer of the 4-aminobutylidene group from dehydrospermidine to putrescine and (c) reduction of the imine intermediate to form homospermidine. This enzyme is more specific than EC 2.5.1.44, homospermidine synthase, which is found in bacteria, as it cannot use putrescine as donor of the 4-aminobutyl group. Forms part of the biosynthetic pathway of the poisonous pyrrolizidine alkaloids of the ragworts (Senecio).
References:
1.  Böttcher, F., Ober, D. and Hartmann, T. Biosynthesis of pyrrolizidine alkaloids: putrescine and spermidine are essential substrates of enzymatic homospermidine formation. Can. J. Chem. 72 (1994) 80–85.
2.  Ober, D. and Hartmann, T. Homospermidine synthase, the first pathway-specific enzyme of pyrrolizidine alkaloid biosynthesis, evolved from deoxyhypusine synthase. Proc. Natl. Acad. Sci. USA 96 (1999) 14777–14782. [PMID: 10611289]
3.  Ober, D., Harms, R. and Hartmann, T. Cloning and expression of homospermidine synthase from Senecio vulgaris: a revision. Phytochemistry 55 (2000) 311–316. [PMID: 11117878]
[EC 2.5.1.45 created 2001]
 
 
EC 2.5.1.46     
Accepted name: deoxyhypusine synthase
Reaction: [eIF5A-precursor]-lysine + spermidine = [eIF5A-precursor]-deoxyhypusine + propane-1,3-diamine (overall reaction)
(1a) spermidine + NAD+ = dehydrospermidine + NADH
(1b) dehydrospermidine + [enzyme]-lysine = N-(4-aminobutylidene)-[enzyme]-lysine + propane-1,3-diamine
(1c) N-(4-aminobutylidene)-[enzyme]-lysine + [eIF5A-precursor]-lysine = N-(4-aminobutylidene)-[eIF5A-precursor]-lysine + [enzyme]-lysine
(1d) N-(4-aminobutylidene)-[eIF5A-precursor]-lysine + NADH + H+ = [eIF5A-precursor]-deoxyhypusine + NAD+
Glossary: deoxyhypusine = N6-(4-aminobutyl)-L-lysine
hypusine = N6-[(R)-4-amino-2-hydroxybutyl]-L-lysine
spermidine = N-(3-aminopropyl)butane-1,4-diamine
Other name(s): spermidine:eIF5A-lysine 4-aminobutyltransferase (propane-1,3-diamine-forming)
Systematic name: [eIF5A-precursor]-lysine:spermidine 4-aminobutyltransferase (propane-1,3-diamine-forming)
Comments: The eukaryotic initiation factor eIF5A contains a hypusine residue that is essential for activity. This enzyme catalyses the first reaction of hypusine formation from one specific lysine residue of the eIF5A precursor. The reaction occurs in four steps: NAD+-dependent dehydrogenation of spermidine (1a), formation of an enzyme-imine intermediate by transfer of the 4-aminobutylidene group from dehydrospermidine to the active site lysine residue (Lys329 for the human enzyme; 1b), transfer of the same 4-aminobutylidene group from the enzyme intermediate to the e1F5A precursor (1c), reduction of the e1F5A-imine intermediate to form a deoxyhypusine residue (1d). Hence the overall reaction is transfer of a 4-aminobutyl group. For the plant enzyme, homospermidine can substitute for spermidine and putrescine can substitute for the lysine residue of the eIF5A precursor. Hypusine is formed from deoxyhypusine by the action of EC 1.14.99.29, deoxyhypusine monooxygenase.
References:
1.  Wolff, E.C., Park, M.H. and Folk, J.E. Cleavage of spermidine as the first step in deoxyhypusine synthesis. The role of NAD+. J. Biol. Chem. 265 (1990) 4793–4799. [PMID: 2108161]
2.  Wolff, E.C., Folk, J.E. and Park, M.H. Enzyme-substrate intermediate formation at lysine 329 of human deoxyhypusine synthase. J. Biol. Chem. 272 (1997) 15865–15871. [PMID: 9188485]
3.  Chen, K.Y. and Liu, A.Y.C. Biochemistry and function of hypusine formation on eukaryotic initiation factor 5A. Biol. Signals 6 (1997) 105–109. [PMID: 9285092]
4.  Ober, D. and Hartmann, T. Deoxyhypusine synthase from tobacco. cDNA isolation, characterization, and bacterial expression of an enzyme with extended substrate specificity. J. Biol. Chem. 274 (1999) 32040–32047. [PMID: 10542236]
5.  Ober, D. and Hartmann, T. Homospermidine synthase, the first pathway-specific enzyme of pyrrolizidine alkaloid biosynthesis, evolved from deoxyhypusine synthase. Proc. Natl. Acad. Sci. USA 96 (1999) 14777–14782. [PMID: 10611289]
6.  Wolff, E.C. and Park, M.H. Identification of lysine350 of yeast deoxyhypusine synthase as the site of enzyme intermediate formation. Yeast 15 (1999) 43–50. [PMID: 10028184]
7.  Wolff, E.C., Wolff, J. and Park, M.H. Deoxyhypusine synthase generates and uses bound NADH in a transient hydride transfer mechanism. J. Biol. Chem. 275 (2000) 9170–9177. [PMID: 10734052]
8.  Joe, Y.A., Wolff, E.C. and Park, M.H. Cloning and expression of human deoxyhypusine synthase cDNA: structure-function studies with the recombinant enzyme and mutant proteins. J. Biol. Chem. 270 (1995) 22386–22392. [PMID: 7673224]
9.  Tao, Y. and Chen, K.Y. Molecular cloning and functional expression of Neurospora deoxyhypusine synthase cDNA and identification of yeast deoxyhypusine synthase cDNA. J. Biol. Chem. 270 (1995) 23984–23987. [PMID: 7592594]
[EC 2.5.1.46 provisional version created 1999 as EC 1.1.1.249 deleted 1999, revised and reinstated 2001 as EC 2.5.1.46]
 
 


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