Genomic identification and biochemical characterization of a second spermidine/spermine N1-acetyltransferase.

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Chen Y, Vujcic S, Liang P, Diegelman P, Kramer DL, Porter CW

Genomic identification and biochemical characterization of a second spermidine/spermine N1-acetyltransferase.

Biochem J. 2003 Aug 1;373(Pt 3):661-7.

PubMed ID

12803540 [ View in PubMed

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Abstract

In the polyamine back-conversion pathway, spermine and spermidine are first acetylated by spermidine/spermine N(1) -acetyl-transferase (SSAT-1) and then oxidized by polyamine oxidase to produce spermidine and putrescine respectively. Herein we apply homology-search methods to identify novel sequences belonging to a second SSAT, SSAT-2, with a chromosomal location at 17p13.1, which is distinct from SSAT-1 at Xp22. Human SSAT-2 cDNA derived from small-cell lung carcinoma was deduced to encode a 170-amino-acid protein having 46% sequence identity and 64% sequence similarity with SSAT-1. When transiently transfected into HEK-293 cells, SSAT-1 decreased spermidine and spermine pools by approximately 30%, while, at the same time, significantly increasing putrescine, N (1)-acetylspermidine, N (1)-acetylspermine and N (1), N (12)-diacetylspermine pools. By contrast, transfected SSAT-2 had no effect on intracellular polyamine or acetylated polyamine pools. When enzyme activity was assayed on enzyme extracts from transfected cells, both SSAT-1 and SSAT-2 demonstrated much higher acetylating activity than vector-transfected cells. The data suggest that, in intact cells, SSAT-2 may be compartmentalized or it may be inefficient at low intracellular polyamine concentrations. By substituting candidate substrates in the enzyme assay, we determined that SSAT-1 shows the substrate preference norspermidine=spermidine>>spermine> N (1)-acetylspermine>putrescine, whereas SSAT-2 shows the preference norspermidine>spermidine=spermine>> N (1)-acetylspermine=putrescine. Analysis of mRNA levels in cell lines and ESTs (expressed sequence tags) from various tissues by digiNorthern (a web-based tool for virtually displaying expression profiles of query genes based on EST sequences) indicated that SSAT-1 tends to be more widely and highly expressed than SSAT-2. While SSAT-1 mRNA was inducible by polyamine analogues in a variety of cell lines, SSAT-2 was not. The existence of an active, but possibly sequestered, SSAT-2 enzyme suggests that, under certain conditions, it may be recruited into basal or perturbed polyamine metabolism.

DrugBank Data that Cites this Article

Drug Enzymes

Drug	Enzyme	Kind	Organism	Pharmacological Action	Actions
Spermine	Diamine acetyltransferase 2	Protein	Humans	Unknown	Substrate	Details

Polypeptides

Name	UniProt ID
Diamine acetyltransferase 2	Q96F10	Details