Phenylalanine metabolism in isolated rat liver cells. Effects of glucagon and diabetes

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Abstract
Methods are described for monitoring the metabolic flux through phenylalanine hydroxylase, the tyrosine catabolic pathway and phenylalanine; pyruvate transaminase in isolated liver cell incubations. The relationship between hydroxylaser flux and phenylalanine concentration is sigmoidal. Glucagon increases hydroxylase activity at low, near-physiological, substrate concentrations only. The hormone does not affect the rate of formation of phenylpyruvate. Experimental diabetes (for 10 days) increases phenylalanine catabolism; this is further increased by glucagon. These results are discussed in light of the known mechanisms for control of phenylalanine hydroxylase activity in vitro.