Abstract
Hypertyrosinemia is often seen in low-birth weight newborn infants and is related to both quantity and quality of protein intake. Tyrosine catabolism may be insufficient due to low activity or incomplete development of tyrosine aminotransferase (EC. 2.6.1.5, TAT). TAT was present in 12 to 17-week-old fetal human liver, the activity being 2.25% of adult human liver (45 and 2000 nmoles/g/min respectively). Liver activities in pre-term and full-term infants of various ages will be presented. The Km for tyrosine was 1.6 × 10-3M and for α-ketoglutarate 3.5 × 10-4M in fetal human liver. The coenzyme pyridoxal-phosphate seemed to be completely dissociable in both fetal and adult enzyme preparations. Iso-electric focusing showed that the fetal enzyme preparation had an activity profile different from that of the adult. The fetal enzyme showed only one major peak whereas the adult had three peaks indicating different subforms of the enzyme. TAT activity could be increased by its substrate, tyrosine (0.5 mM) in fetal liver explants maintained in organ culture. Studies on the perinatal regulation of enzyme activities and levels in human tissues are of importance in light of the clinical attempts to enhance enzyme differentiation in functionally immature infants.
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Andersson, S., Ohisalo, J. & Räihä, N. Tyrosine aminotransferase in human Liver; development, properties and substate induction in organ culture. Pediatr Res 13, 78 (1979). https://doi.org/10.1203/00006450-197901000-00051
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DOI: https://doi.org/10.1203/00006450-197901000-00051
