Where is the GABA transaminase (responsible for GABA catabolism) located in the mammalian brain? I understand that the enzyme responsible for GABA synthesis, GAD, is in the terminal boutons. But I am wondering, if GABA-containing vesicles are sitting in the boutons and kept there, is the GABA at any immediate risk of being broken down, before it has the chance to traverse the cleft?
It's my understanding that GABA-transaminase is basically ubiquitous, in mitochodrial and plasma membranes and cytoplasmic matrix, more concentrated in neurons than glia. There is some fairly early literature (late 70s, 80s) that use immunohistochemistry to show GABA-Tase distribution.
On another note, I would draw attention to the two different forms of GAD, I think 65 and 67. These have different subcellular distributions and are putatively differentially involved in the production of GABA in the shunt of the TCA cycle of respiration (intra-cellular) and in neurotransmitter production (closer to the synapse).
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