The series of molecular signals initiated by an extracellular ligand binding to a receptor on the surface of the target cell, where the receptor possesses catalytic activity or is closely associated with an enzyme such as a protein kinase, and ending with the regulation of a downstream cellular process, e.g. transcription. [ https://www.worldcat.org/search?q=bn%3A0815316194 GOC:mah GOC:signaling ]