How to set srid of a single point coordinates pair using PostGis?

I think is better explain with a small example: selected a geometry point i get it back in a coordinates pair

SELECT ST_AsGeoJSON('010100002031BF0D009A999919F9BD2D41CDCCCC4C758E5241')
--result:
"{"type":"Point","coordinates":[974588.55,4864469.2]}"

to return back the geometry simply i make

SELECT ST_GeometryFromText('POINT(974588.55 4864469.2)')

having for example the same pair of geographic coordinates in degrees

coordinates:[9.7458855,48.644692]}

How can i transform them into the previous pair format and get the starting geometry?

I'm working with leaflet and i would implement a kind of routing service using pgRouting, I have populated postgis with "osm2pgsql" tool and all geometries are of 900913 SRID type. My goal is to compare the source and target points on a map with the vertices stored in postgres. Applying a transformation on a point picked from the map to 900913 srid don't get me the right thing, also i notice that the last four numbers (5241) are the same for each geometry in the db and them are different when i transform the geometry returned from my point, what they refer?