In Vitro SSAT Enzyme Activity Study Using Rat and Mouse Liver Tissue Preparations
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Spermidine/spermine N1-acetyltransferase (SSAT) is the enzyme which acetylates spermidine (Spd) to acetylspermidine (AcSpd). SSAT is also capable of acetylating polyamine analogues such as triethylenetetramine (TETA) to acetyltriethylenetetramine (MAT). However, this process is debatable because while the overexpression of Spermidine/spermine N1-acetyltransferase (SSAT1) increases the MAT level, the knockout of SSAT1 remains the same MAT level as the non-treatment groups. This research was designed to establish a method to precisely measure the activity of SSAT via the quantification of the metabolites resulting from SSAT catalysis by using spermidine-D6 (Spd-D6), the stable isotope of Spd, to get rid of the disturbance from endogenous Spd. In vitro polyamine acetylation assay was applied to measure the SSAT enzyme activity by using Spd-D6 as the substrate. This research developed a liquid chromatography-mass spectrometry (LC-MS) method to detect the metabolites, acetylspermidine-D6 (AcSpd-D6). This research not only measured the acetylation activity of enzyme from different tissue origin with various polyamine substrates, but also compared them with the results of different non-enzymatic controls. The results presented that non-enzymatic controls were showing polyamine acetylation activities. Standard curves were not showing obvious differences, which means the enzyme sources were not influencing the LC-MS detection. In conclusion, the role of SSAT may be: 1) SSAT inhibits AcCoA from reacting with other substances. 2) SSAT accelerates the transportation of AcCoA from mitochondria to the cytoplasmic matrix. 3) SSAT is a carrier protein which transports AcCoA to other cellular locations.