Haruko Goto

AMP deaminase isozymes in human tissues

In human, there are four AMP deaminase (AMP aminohydrolase, EC 3.5.4.6) isozymes: E1, E2, M and L. Chromatographic, electrophoretic and immunological studies showed the existence of isozymes E1 and E2 in erythrocytes, isozyme M in muscle and isozyme L in liver and brain. The tissues such as heart, kidney and spleen contained isozymes E1, E2 and L. Isozymes E1, M and L were isolated as apparently homogeneous preparations. The three isozymes were all tetramers composed of identical subunits, but differing slightly in molecular weight; isozyme E1 showed a subunit molecular weight of 80,000, isozyme M 72,000 and isozyme L 68,000. They were immunologically different from one another. The antisera precipitated only the corresponding enzyme and did not precipitate any other isozyme. The three isozymes were also different in kinetic and regulatory properties. Isozyme E2 was very similar to isozyme E1 in immunological an kinetic properties, although isozyme E2 could be separated from isozyme E1 by phosphocellulose chromatography, and zonal electrophoresis.

Isozymes of rat AMP deaminase.

Three AMP deaminase isozymes (EC 3.5.4.6 AMP aminohydrolase) were purified from rat heart, kidney and muscle. These enzyme preparations contained only the required isozyme. Antisera to individual isozymes were prepared and immunological relationships were tested. There was no cross-reactivity as tested by precipitation experiments. The antisera precipitated only the corresponding isozyme and there was no effect on other isozymes. These isozymes were also different in Km values for AMP and in substrate specificity. From the present studies, combined with previous results, it seems clear that the heart, kidney and muscle enzymes are different basic types. It is proposed that the muscle enzyme be designated as AMP deaminase A; the enzyme in kidney and liver, AMP deaminase B; the enzyme in heart, AMP deaminase C. Brain extracts contained five isozymes; two parent isozymes (B and C) and presumably their three hybrids.

Molecular analysis of five independent Japanese mutant genes responsible for hypoxanthine guanine phosphoribosyltransferase (HPRT) deficiency

Five independent mutations in the hypoxanthine guanine phosphoribosyltransferase (HPRT) gene were identified in a partially HPRT deficient patient with gout and in four Lesch-Nyhan patients. Using the polymerase chain reaction (PCR) technique coupled with direct sequencing, the nucleotide sequences of the entire HPRT coding region amplified from the cDNA and also of each exon amplified form the genomic DNA were analyzed. Three independent point mutations in the coding region were detected in the partially HPRT deficient patient (Case 1) and in two Lesch-Nyhan patients (Case 2 and 3), resulting in single amino acid substitutions. The family study of Case 3, utilizing a PvuII restriction site created in the mutant gene, indicated that the mother was a heterozygote, and a sister and a fetal brother had inherited the normal HPRT gene from the mother. In two other mutants causing Lesch-Nyhan syndrome, a portion of the HPRT gene was deleted, and RNA splicing was missing in both mutants. A 4-bp deletion at the 5′ end of exon 4 resulted in formation of three different types of abnormal mRNA (Case 4). The other mutant (Case 5) produced abnormal mRNA including 26bp of intron 8 instead of the deleted 58bp at the 5′ end of exon 9, because of a 74-bp deletion from intron 8 to exon 9.

MOLECULAR ANALYSIS OF EXTRACELLULAR-SUPEROXIDE DISMUTASE GENE ASSOCIATED WITH HIGH LEVEL IN SERUM

SummaryExtracellular-superoxide dismutase (EC-SOD) is one of the SOD isozymes mainly distributed in the extracellular fluid. In the vascular system, it is located on the endothelial cell surface according to studies on the heparin binding capacity. By measurement of serum EC-SOD levels of Japanese in healthy persons (n=103) and hemodialysis patients (n=150), 7 healthy subjects and 24 hemodialysis patients were classified into group II associated with high EC-SOD levels. By molecular analysis of the EC-SOD coding region from the group II individuals in Sweden, a single nucleotide substitution of G to C generating an amino acid change of arginine to glycine has been identified in the region associated with the heparin affinity of the enzyme. The same mutation was detected in the Japanese as a homozygote in both alleles of 2 hemodialysis patients and as a heterozygote in one allele of all the healthy group II individuals and 17 hemodialysis patients. The amino acid substitution may result in the decrease of the heparin affinity which is favorable for the existence of EC-SOD in the serum.

Complete deficiency of AMP deaminase in human erythrocytes

Four individuals with complete absence of erythrocyte AMP deaminase have been discovered. The subjects appear to be perfectly healthy and there was no evidence of hemolysis. The deficiency was found only in erythrocytes and as expected, mononuclear cells and platelets showed normal level of activity. The activities of all the other purine metabolizing enzymes that were tested were normal. The deficiency is inherited as an autosomal recessive trait.

Deficiency of AMP deaminase in erythrocytes

SummarySix individuals with complete deficiency of erythrocyte AMP deaminase have been discovered. They are all healthy and have no hematological disorders. The deficiency is only in isozyme E, which is the erythrocyte type isozyme, and is inherited as an autosomal recessive trait. The frequency of the mutant gene is surprisingly high, one heterozygote in about 30 of the population in Japan, Seoul, and Taipei. The ATP level is approximately 50% higher in AMP-deficient erythrocytes compared to that of control cells. Degradation of adenine nucleotide is slower in the deficient erythrocytes than in the control erythrocytes.

Isozymes of rat brain AMP deaminase: Developmental changes and characterizations of five forms

AMP deaminase is known to be physiologically important in the stabilization of energy charge [ 11, interconversion of adenine, inosine and guanine nucleotides [2-51 and furthermore as a key enzyme in the purine nucleotide cycle [6-~81. The deaminase exists in multiple molecular forms in different rat tissues [9-121. On the basis of chromatographic, immunological, and kinetic properties, three parental forms (Types A, B and C) have been detected [11,12]. Type A AMP deaminase is the only form found in skeletal muscle; Type B, the major isozyme of kidney and liver; Type C, the form found in heart. Previous studies demonstrated that there are five different chromatographic forms of AMP deaminase in the adult rat brain; they have been designated as isozymes I through V on the basis of order of elution from the column [ 121. lsozymes I and V correspond in elution position to the only isozyme found in cardiac tissue and to the major component found in kidney and liver, respectively. In this paper we report the changes of AMP deaminase isozymes in developing rat brain and also the studies on the interrelationship between the properties of the isozymes found in adult rat brain.

Bilirubin: A potent inhibitor of NAD+-linked isocitrate dehydrogenase

Bilirubin was found to be a potent inhibitor of NAD+-linked isocitrate dehydrogenase (threo-ds-isocitrate:NAD+ oxidoreductase (decarboxylating), EC 1.1.1.41). It inhibited the enzyme by decreasing the affinity of enzyme for isocitrate, while the maximum reaction velocity was not affected. Bilirubin (less than 10−6 M) showed a detectable inhibition. On the other hand, neither the mitochondrial nor the cytoplasmic NADP+ enzymes (threo-ds-isocitrate:NADP+ oxidoreductase ((decarboxylating), EC 1.1.1.42) were affected by bilirubin.

Polymorphism of extracellular superoxide dismutase (EC-SOD) gene: relation to the mutation responsible for high EC-SOD level in serum.

SummaryExtracellular superoxide dismutase (EC-SOD) with amino acid substitution R213G generated by the nucleotide substitution 760C→G in the heparin binding domain is responsible for the high EC-SOD level in serum. We identified the two DNA polymorphic sites in the coding region of EC-SOD gene related to the 760C→G and determined the allele frequencies. The polymorphisms were A and G at nucleotide position (nt.) 241 and C and T at nt. 280 near the N-terminal. The haplotype frequencies in Japanese were 241A280C: 0.45, 241G280T: 0.37, and 241G280C: 0.18. The haplotype of 241A280T did not exist. The mutation 760C→G must occur on the allele having the haplotype of 241G280T.

Subunit structures of AMP deaminase isozymes in rat

Abstract AMP deaminases A and B have been purified to apparent homogeneity from rat muscle and liver, respectively. The molecular weights of 286,000 and 351,000 were obtained for the native muscle and liver enzymes, respectively, by sedimentation equilibrium studies. On polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, the muscle preparation exhibited a single polypeptide band with a molecular weight of 72,000; the liver preparation, a molecular weight of 85,000. The data indicate that each enzyme has a tetrameric structure.