{'fraction_non_alphanumeric': 0.03780718336483932, 'fraction_numerical': 0.013232514177693762, 'mean_word_length': 5.086206896551724, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Serine phosphorylation of the secreted extracellular domain of APP.

The phosphorylation status of full-length APP (FL-APP) and secreted APP (s-APP) was investigated in stably transfected cells. 32P incorporation was detected in the mature full-length APP both in the absence and presence of phorbol ester. Surprisingly, 32P-phosphate was incorporated in the secreted ectodomain, and this was stable to treatment of the [32P]-phospho-s-APP with a large excess of PNGase F, suggesting that N-linked oligosaccharide sites do not account for phosphate incorporation. Phosphoamino acid analysis of the [32P]-phospho-s-APP resulted in the recovery of [32P]-phosphoserine as the preponderant species. Brefeldin A completely inhibited the release of [32P]-phospho s-APP, but did not inhibit the incorporation of 32P into the FL-APP, suggesting that phosphorylation occurs early in the central vacuolar pathway. It is possible that ectodomain phosphorylation by a novel luminal or extracellular protein kinase may play a role in regulating the metabolic fate of APP.