Glycyl-L-glutamine, a precursor, and glycyl-L-glutamic acid, a neurotrophic factor for maintenance of acetylcholinesterase and butyrylcholinesterase in the preganglionically denervated superior cervical ganglion of the cat in vivo.

Abstract

(11) showed recently that ,B-endorphin inhibits the formation of A12 AcChoEase from smaller aggregates in cultured immature rat muscle. On the other hand, the dipeptide glycyl-L-glutamine (Gly-Gln), which is formed by endopeptidase cleavage of the terminal of P-endorphin (12), was found by Haynes and Smith (13) to enhance markedly the formation of A12 and G4 AcChoEase in cultured embryonic rat and chicken skeletal muscle. Since Gly-Gln meets the criteria for the endogenous NF established for the cat SCG in vivo (8), it was examined by this procedure. Present results indicated that Gly-Gln itself, by the cat in vivo assay, is inactive as a NF, but that a metabolite is probably highly active. The three most likely metabolites were therefore tested: glycine, L-glutamine, and glycyl-L-glutamine acid (Gly-Glu). The first two were found to be inactive, the last (Gly-Glu) highly active.We have also included a comparison of the currently employed method of extraction of SCG by homogenization in distilled water for assay of AcChoEase, BtChoEase, and protein contents with a procedure widely used at present in which the enzymes are solubilized with molar NaCl/1% Triton X-100 (e.g., ref. 14). METHODSAnesthetic and surgical procedures and the methods for homogenization of ganglia and for determination of their AcChoEase, BtChoEase, and protein contents and for calculation of statistical significance of mean differences were identical with those reported (3). Under sodium pentobarbital anesthesia (35 mg/kg, intraperitoneally) 1 cm was resected from both cervical sympathetic trunks; the wound was sutured and Combiotic (penicillin/dihydrostreptomycin, Pfizer, 0.5 ml, intramuscularly) was given. The following day cats were again anesthetized as before and atropinized (1.0

L-glutamic acid, a neurotrophic factor for maintenance of acetylcholinesterase and butyrylcholinesterase in the preganglionically denervated superior cervical ganglion of the cat.

“…Values (Tables 3 and 4 in ref. 5) were considerably higher than those found here or previously (9) with authentic compounds. The present findings are also inconsistent with the earlier conclusion that the endogenous neurotrophic factor is probably a peptide (5).…”

“…Negative results were obtained here with glycine plus glutamine, and with pyroglutamic acid, GABA, and aspartic acid, and previously with glycine and glutamine individually (9). In an earlier study (5), negative results were found also with acetylcholine and nerve growth factor (7S and 2.5S), and findings were borderline with cyclic AMP.…”

“…It was found previously that glycine and L-glutamine, two possible metabolites of glycyl-L-glutamine, were inactive as neurotrophic factors (9). The combination of both at 10 and 100 ,uM each was shown here to be ineffective (Table 2, cats G and H).…”

“…The neurotrophic action demonstrated previously with glycyl-L-glutamic acid (9) (23). Recently, some new dicarboxylic amino acid receptors have been discovered in rat hippocampus that couple with guanyl cyclase and with phosphatidylinositide-specific phospholipase A; the latter catalyzes the formation ofinositol phosphates (24).…”

“…Results indicated that a metabolite of Gly-Gln is an active neurotrophic factor. Of three possible metabolites tested, glycine and L-glutamine were found to be inactive but glycyl-L-glutamic acid (GlyGlu) was significantly active (9).…”