A catalyst that regulates the rate at which chemical reactions proceed in living organisms without itself being altered in the process. *

enzyme
nucleic acid
carbohydrate
base

I think the answer is enzyme : )

Neurotransmitters are messengers responsible for communication between neurons. they are released from synaptic vesicles and are received by receptors.  the communication is referred to as neurotransmission. the following statement is true about neurotransmitters: a. they're stored in synaptic vesicles in the axon.