Parvin Justice

The metabolism of 5-hydroxytryptamine (serotonin) in the newborn.

Infants have lower values of 5-hydroxytryptamine than do adults. This is related to the age and weight of the infants; adult values can be achieved by the administration of pyridoxine. Newborn rats have low concentrations of 5-hyroxytrypiophan decarboxylase in their kidneys; this was prolonged when their mothers were placed on a pyridoxine-deficient diet. Low levels of 5-hydroxytryptamine represent immaturity of the apoenzyme at birth and a relative deficiency of pyridoxine.

A defect in tryptophan metabolism.

Extract: Oral tryptophan loading tests were performed in a patient with photosensitive pellagra-like skin rash and cerebellar ataxia but without hyperaminoaciduria. Plasma tryptophan concentrations after loading were similar in the patient and control subjects. Average urinary excretion of tryptophan in the patient from 0 to 6 and 6 to 12 hr was 2.69 and 2.58 μmol/kg, respectively; that in the control subjects was 0.82 and 0.34 μmol/kg, respectively. However, the average renal clearance of tryptophan during the first 6 hr of the loading tests in the patient was 0.757 ml plasma/1.73 m2 and that in the control subjects was 0.706 ml plasma/1.73 m2.Renal excretion of kynurenine in the patient was markedly decreased. The average from 0 to 6 and 6 to 12 hr in the patient was 1.90 and 1.13 μmol/kg, respectively; that in the control subjects was 12.90 and 18.15 μmol/kg, respectively. Under ultraviolet light, paper chromatograms of urine from the patient showed a deficiency of xanthurenic acid, kynurenic acid, kynurenine, and formylkynurenine. The deficiency of formylkynurenine in the patients urine was confirmed by staining the paper chromatograms with Ehrlichs reagent.The patient was “sensitive” to oral nicotinic acid treatment; however, oral nicotinamide was well tolerated with improvement in the photosensitive skin rash.Speculation: The normal absorption of tryptophan and the marked decrease of formylkynurenine and kynurenine in the urine after tryptophan loading in this patient suggest a metabolic block in tryptophan oxidation. The lack of formylkynurenine excretion suggests a deficiency of tryptophan pyrrolase (L-tryptophan 2,3-dioxygenase).

Purification and characterization of genetic variants of 6-phosphogluconate dehydrogenase

This paper describes the physicochemical characteristics in partially purified enzyme on subjects with the Pd A, Pd AB, and Pd B variants of 6-phosphogluconic dehydrogenase (6PGD). For these studies, whole blood was purified about 225-fold using ion exchange chromatography on DEAE cellulose column and fractionation with ammonium sulfate. 6PGD emerges as a single peak between 0.01 m and 0.1 m phosphate buffer on the column and is precipitated in the 55–80% fraction of ammonium sulfate. This purified enzyme can be stored frozen for several months without appreciable loss of activity and contains no detectable activity of glucose 6-phosphate dehydrogenase and glutathione reductase. The three variants of partially purified 6PGD varied from each other in two respects. The transitional temperature is 47.8 C for Pd A, 45.4 C for Pd AB, and 41.1 C for Pd B. The Km for 6PGA is 30 μm for Pd A, 21 μm for Pd AB, and 15 μmfor Pd B. These observations add further strength to the concept that the polymorphism in 6PGD represents alterations in either the configuration or structure of the protein molecule itself.

Electrophoretic mobility of glucose-6-phosphate dehydrogenase in lymphocytes and granulocytes

Abstract The electrophoretic mobility of glucose-6-phosphate dehydrogenase (G-6-P D) was determined utilizing enzymes from total white blood cells as well as pure populations of polymorphonuclear leukocytes and lymphocytes. The enzyme from the cell fractions was partially purified and characterized. Although different electrophoretic mobilities were found for G-6-P D from lymphocytes and polymorphonuclear leukocytes, the physiochemical characteristics were found to be similar.

STUDIES ON INHIBITION OF BRAIN 5-HYDROXYTRYPTOPHAN DECARBOXYLASE BY PHENYLALANINE METABOLITES.

Summary The Km for brain 5HTPD is 5.2 × 10-5 M. The inhibition of this enzyme by phenylalanine derivatives is competitive and substrate-dependent at pH 8.05. This inhibition does not appear to play a major role in the decrease of brain 5HT reported in experimental phenylketonuria. The authors wish to express their appreciation to Dr. M. W. McOaman for helpful advice and Joan Gordon for technical assistance.

72 Phenylalanine Hydroxylase Activity in Hyperphenylalanernia

The recent widespread screening for phenylketonuria among newborn infants has lead to the recognition that not all instances of hyperphenylalanemia is caused by phenylketonuria (PKU). Thispaper describes enzyme studies in four patients with hyperphenylalanemia.Case 1 is a patient with ‘classical’ PKU. Case 2 is an infant who was found to have a plasma phenylalanine (PPA) of 17 mg% at three weeks who showed ‘mild’ PKU. Case 3 is a 35y-ear-old retarded female with PPA values ranging from 6.6 mg % to 11.6 mg % on a regular diet. Case 4 is an infant with a PPA value of 45 mg % at 4 days and 76.4 mg % at 2 ½ weeks. She was treated with low-phenylalanine diet for 15 months and then returned to a regular diet. For the past 7 months on a regular diet, the PPA has ranged between 4.6 mg % and 10.7 mg %. Cases 3 and 4 may be viewed as hyperphenylalanemia without PKU.Phenylalanine hydroxylase was determined by the method of LaDu and Zannoni and fresh liver obtained by biopsy. The results expressed as μM tyrosine14C formed/Gm protein/45 minutes were as follows:These data suggest that the ‘classical’ and ‘mild’ form of PKU probably have the same basic metabolic lesion. They show that hyperphenylalanemia without PKU is not caused by cofactor deficiency and represents a true ‘partial’ PKU as reflected by slightly elevated PPA, delayed clearance of phenylalanine by tolerance test and decrease of phenylalanine hydroxylase in liver. (APS)