what is acyl coa synthase and how does it function in convertion of fatty acid to acyl coa(coenzyme a)?

I am quoting the following from the textbook:"Before fatty acids can be oxidized, they must be "primed" for reaction in an ATP-dependent acylation reaction to form fatty acyl-CoA.  This activation process is catalyzed by a family of at least three acyl-CoA synthetases (also called thiokinases) that differ according to their chain-length specificities.  These enzymes, which are associated with either the endoplasmic reticulum or the outer mitochondrial membrane, all catalyze the reaction:

Fatty acid + CoA + ATP <=> acyl-CoA + AMP = PPi"

A couple of comments:

First, fatty acids are NOT converted to Coenzyme a, but rather, require coenzyme a for their metabolism.

Second, synthetase is synonymous with synthase.

Hope this was helpful for you.  Best wishes.