"Specific substrates" refers to particular materials or substances that are required or used in a specific process, reaction, or function. Full definition
Many other researchers have built sensors for detecting biomolecules, which use enzymes» ability to recognise specific substrate molecules. (newscientist.com)
The enzyme pocket has a special shape so that only one specific substrate is able to bind to it, just like only one key fits into a specific lock. (scientificamerican.com)
McsB has been known to be transcriptionally co-regulated with a major protease of the bacterium B. subtilis, ClpCP, and was once proposed to function as its «adaptor» that brings in a specific substrate. (sciencedaily.com)