Schiff Base in Enzyme Mechanisms
I think the answer to this one is a most definite 'yes'.  Almost all aminotransferases proceed via a ping-pong mechanism where a schiff base involving pyridoxal phosphate is an obligate intermediate, and where  the 'half-reation' modified enzyme form has often been isolated. An example is aspartate aminotransferase.

Let's also remind ourselves that a transition state is not an intermediate on the reaction pathway (in the TS bonds are in the process of being broken and formed), but may resemble one.