{'fraction_non_alphanumeric': 0.05413533834586466, 'fraction_numerical': 0.0406015037593985, 'mean_word_length': 4.324, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 1, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Part of the phospho group of pyridoxal phosphate may titrate over the pH range 5-8 in aspartate aminotransferase.

The 31P n.m.r. spectrum of aspartate aminotransferase (EC 2.6.1.1) shows a pK of about 6.5 (the value varies with isoenzyme and with salt concentration) in the pH-dependence of the chemical shift of the phosphorus atom of the pyridoxal phosphate. When this was first observed, it was attributed to titration between -PO3Hand-PO32-; it was soon realized, however, that the change in shift was too small for this conversion (Mattingly et al., 1982; Korpela et al., 1987a,b; Schnackerz et al., 1989; Sanchez-Ruiz et al., 1991). These three groups of authors therefore concluded (1) that the group was in the -PO32form throughout the pH range 5-8 [Sanchez-Ruiz & Martinez-Carrion (1986) and Sanchez-Ruiz et al. (1991) qualified this by saying merely that it was mainly in the dianionic form], and (2) that an ionization of pK 6.5 elsewhere in the protein was affecting the phosphorus, e.g. by changing G-P-O bond angles. Although the arguments were convincing that complete titration of -PO3Hto -PO32would give a much larger change in chemical shift than that observed, no one argued whether a fraction of the group might not possess the observed pK. Dixon & Tipton (1973) pointed out that, to a close approximation, 64