The entire brain posses the enzymes needed to synthesize DMT from tryptamine. The enzyme is called N-methyl-transferase, it uses SAM-e as a co-enzyme. Although other enzymes are reported with different co-enzymes. 5-MeO-tryptamine has been found in the pineal as would be expected as it is a precursor to melatonin. Also various beta-carbolines have also been found in the pineal.
Endogenous DMT has NOT been shown to bind to the Sigma-1 receptor in the normal functioning body. Although DMT does bind to the receptor and thus this site may be involved in some of the subjective effects of administered DMT. A variety of drugs bind to Sigma receptors, in fact most drugs do (cocaine, hormones, anti-psychotics, amphetamines....) . Sigma-1 is a strange receptor and many factors make it unlikely to be the endogenous site of DMT. It does not appear to be a neurotransmitter receptor but rather a intracellular regulator protein. Although more work needs to be performed.