Effect of pyridoxal phosphate deficiency on aromatic L-amino acid decarboxylase activity with L-dopa and L-5-hydroxytryptophan as substrates in rats.

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Abstract
The distribution of aromatic L-amino acid decarboxylase (AADC) activities in 14 tissues (8 peripheral tissues and 6 brain regions) of semicarbazide(SC)-treated rats was investigated using both L-dopa and L-5-hydroxytryptophan (L-5-HTP) as substrates. The distribution of pyridoxal phosphate (PLP) was also measured in control and SC-treated rats. SC-treatment decreased the PLP concentration in all tissues (about 50-60% of control). AADC activities towards L-dopa and L-5-HTP as substrates were also decreased significantly in almost all tissues of SC-treated rats. After the addition of exogenous PLP in vitro, AADC activities were recovered only partially in most tissues, but the recovery patterns were not parallel between L-dopa and L-5-HTP as substrates. L-Dopa decarboxylase activity was more sensitive to PLP-deficiency than L-5-HTP decarboxylase activity in the same tissues. Serum AADC activities were decreased drastically using both L-dopa and L-5-HTP as substrates. No serum AADC activity was detected in SC-treated rats using L-dopa as substrate, but low activity was detected in the same sample using L-5-HTP as the substrate; both activities recovered completely after in vitro addition of 10 .mu.M PLP in the incubation mixtures.
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