The chemistry in the central regions of galaxies is expected to be strongly influenced by their nuclear activity .
To find the best tracers of nuclear activity is of key importance to understand the processes taking place in the most obscured regions of galactic nuclei .
In this work we present multi-line observations of CS , C ^ { 34 } S , HNCO and C ^ { 18 } O in a sample of 11 bright galaxies prototypical for different types of activity .
The ^ { 32 } S/ ^ { 34 } S isotopic ratio is \sim 10 , supporting the idea of an isotopical ^ { 34 } S enrichment due to massive star formation in the nuclear regions of galaxies .
Although C ^ { 32 } S and C ^ { 34 } S do not seem to be significantly affected by the activity type , the HNCO abundance appears highly contrasted among starburst .
We observed HNCO abundance variations of nearly two orders of magnitude .
The HNCO molecule is shown to be a good tracer of the amount of molecular material fueling the starburst and therefore can be used as a diagnostics of the evolutionary state of a nuclear starburst .