Regional distribution and biochemical properties of 125I-Tyr8-substance P binding sites in synaptic vesicles.

1. Binding of 125I-Tyr8-substance P (SP) to synaptic vesicles shows an uneven distribution within the brain and the spinal cord. The regional distribution has a positive correlation with the SP-content, except in the hypothalamus. 2. Ca2+ and MG2+-ions (1 and 10 mM) decrease the number of binding sites without alteration of affinity. EDTA and EGTA enhance SP-binding which is interpreted as being due to removal of the inhibitory influence of endogenous Ca2+ and Mg2+ through chelation with these agents. No significant inhibition of SP binding was observed by Na+ or K+ in concentrations below 100 mM. 3. Pretreatment of synaptic vesicles with trypsin or with phospholipase A2, C and D leads to a total loss of SP binding showing a proteolipid or a joint protein-phospholipid nature of these binding sites. SH groups do not contribute to SP binding since no effect of N-ethylmaleimide and monoidoacetic acid on SP binding was found.