A simple assay for methionine adenosyltransferase using cation exchange paper and liquid scintillation spectrometry

Effects of high dietary methionine on activities of selected enzymes in the liver of kittens (Felis domesticus)

1. Growing male kittens were fed an 18% casein diet supplemented with 2, 3, or 4% L-methionine (MET) for 6 weeks. 2. Free MET concentration in liver increased 30-fold and cystathionine two- to three-fold; the activity of adenosyl-MET transferase and cystathionase also increased but remained lower than previously found in rats. 3. Taurine concentration in liver decreased in cats fed excess MET and appeared to depend on taurine intake. 4. Alanine aminotransferase activity was high in all groups while serine dehydratase activity was very low. 5. Pyruvate kinase and malic enzyme activities which are normally low in cat liver increased after excess MET. Also, glucose 6-phosphate and 6-phosphogluconate dehydrogenases increased. 6. Cat liver metabolism showed limited adaptation to an excess dietary intake of methionine compared to that found in rats.

Down-regulation of rat liver beta-adrenergic receptors by cysteine

Down-regulation of hepatic beta-adrenergic receptors was indicated by a 56% decrease in the specific activity of 125I-iodocyanopindolol bound to rat liver membrane preparations from rats fed diets containing 15% of casein supplemented with cysteine, instead of methionine or unsupplemented. Down-regulation of hepatic beta-adrenergic receptors by cysteine appears to be mediated through an effect of cysteine on the tissue concentration of S-adenosyl methionine (SAM). The liver tissue concentration of SAM in rats fed cysteine-supplemented diets decreased 53% compared to those fed diets supplemented with methionine. The decrease in liver SAM in rats fed the diet supplemented with cysteine appears to reflect a non-competitive inhibition of methionine adenosyl-transferase by cysteine. Lineweaver-Burk plots demonstrated a dose-related Vmax response to cysteine but did not change the apparent Km at any concentration tested.

The influence of nerve section on the metabolism of polyamines in rat diaphragm muscle

Concentrations of spermidine, spermine and putrescine have been measured in rat diaphragm muscle after unilateral nerve section. The concentration of putrescine increased approx. 10-fold 2 days after nerve section, that of spermidine about 3-fold by day 3, whereas an increase in the concentration of spermine was only observed after 7-10 days. It was not possible to show enhanced uptake of either exogenous putrescine or spermidine by the isolated tissue during the hypertrophy. Consistent with the accumulation of putrescine, activity of ornithine decarboxylase increased within 1 day of nerve section, was maximally elevated by the second day and then declined. Synthesis of spermidine from [14C]putrescine and either methionine or S-adenosylmethionine bt diaphragm cytosol rose within 1 day of nerve section, but by day 3 had returned to normal or below normal values. Activity of adenosylmethionine decarboxylase similarly increased within 1 day of nerve section, but by day 3 had declined to below normal values. Activity of methionine adenosyltransferase was elevated throughout the period studied. The concentration of S-adenosylmethionine was likewise enhanced during hypertrophy. Administration of methylglyoxal bis(guanylhydrazone) produced a marked increase in adenosylmethionine decarboxylase activity and a large increase in putrescine concentration, but did not prevent the rise in spermidine concentration produced by denervation. Possible regulatory mechanisms of polyamine metabolism consistent with the observations are discussed.

Isolation of a metK mutant with a temperature-sensitive S-adenosylmethionine synthetase

An Escherichia coli metK mutant, designated metK110, was isolated among spontaneous ethionine-resistant organisms selected at 42 degrees C. The S-adenosylmethionine synthetase activity of this mutant was present at lower levels than in the corresponding wild-type strain and was more labile than the wild-type enzyme when heated or dialyzed. A mixture of mutant and wild-type enzyme preparations had an activity equal to the sum of the component activities. These facts strongly suggest that the mutated gene in this strain is the structural gene for this enzyme. Genetic mapping experiments placed the metK110 mutation near or at the site of other known metK mutants (i.e., 63 min), confirming its designation as a metK mutant. A revised gene order has been established for this region, i.e., metC glc speC metK speB serA.

S-adenosylmethionine metabolism and its relation to polyamine synthesis in rat liver. Effect of nutritional state, adrenal function, some drugs and partial hepatectomy

S-Adenosylmethionine metabolism and its relation to the synthesis and accumulation of polyamines was studied in rat liver under various nutritional conditions, in adrenalectomized or partially hepatectomized animals and after treatment with cortisol, thioacetamide or methylglyoxal bis(guanylhydrazone) {1,1'-[(methylethanediylidine)dinitrilo]diguanidine}. Starvation for 2 days only slightly affected S-adenosylmethionine metabolism. The ratio of spermidine/spermine decreased markedly, but the concentration of total polyamines did not change significantly. The activity of S-adenosylmethionine decarboxylase initially decreased and then increased during prolonged starvation. This increase was dependent on intact adrenals. Re-feeding of starved animals caused a rapid but transient stimulation of polyamine synthesis and also increased the concentrations of S-adenosylmethionine and S-adenosylhomocysteine. Similarly, cortisol treatment enhanced the synthesis of polyamines, S-adenosylmethionine and S-adenosylhomocysteine. Feeding with a methionine-deficient diet for 7-14 days profoundly increased the concentration of spermidine, whereas the concentrations of total polyamines and of S-adenosylmethionine showed no significant changes. The results show that nutritional state and adrenal function play a significant role in the regulation of hepatic metabolism of S-adenosylmethionine and polyamines. They further indicate that under a variety of physiological and experimental conditions the concentrations of S-adenosylmethionine and of total polyamines remain fairly constant and that changes in polyamine metabolism are not primarily connected with changes in the accumulation of S-adenosylmethionine or S-adenosylhomocysteine.

Tissue distribution of S-adenosylmethionine and S-adenosylhomocysteine in the rat. Effect of age, sex and methionine administration on the metabolism of S-adenosylmethionine, S-adenosylhomocysteine and polyamines

The tissue distribution of S-adenosylmethionine, S-adenosylhomocysteine, methionine adenosyltransferase and S-adenosylhomocysteine hydrolase was explored in the rat. Also the effects of methionine administration on the accumulation of S-adenosylmethionine, S-adenosylhomocysteine and polyamines were studied in rat liver, brain and kidney. The tissue distribution of S-adenosylmethionine, S-adenosylhomocysteine, methionine adenosyltransferase and S-adenosylhomocysteine hydrolase was similar in both sexes, and was only slightly changed with age. The specific activity of S-adenosylhomocysteine hydrolase greatly exceeded that of methionine adenosyltransferase, and the concentration of S-adenosylmethionine was higher than that of S-adenosylhomocysteine in all tissues examined. However, the hepatic S-adenosylmethionine/S-adenosylhomocysteine ratio was dependent on food supply and on the age of the animal. No correlation was noticed between the activity of methionine adenosyltransferase and the concentrations of the adenosyl compounds in different tissues. Intraperitoneal administration of methionine resulted in a profound but transient increase in the hepatic concentrations of S-adenosylmethionine and S-adenosylhomocysteine. The concentration of S-adenosylmethionine was elevated also in the brain during the first 2h after methionine injection. The rise of S-adenosylmethionine concentration after methionine treatment could be diminished by simultaneous glycine administration. The results support the view that the rate-limiting factor of S-adenosylmethionine synthesis is the tissue concentration of methionine. They further suggest that glycine N-methyltransferase may have a regulatory role in the utilization of S-adenosylmethionine in the liver.

Isolation and characterization of specialized lambda transducing bacteriophage carrying the metBJF methionine gene cluster

Secondary attachment site lysogens of Deltaatt(lambda)Deltappc-argECBH strains of Escherichia coli with lambdacI857 integrated into the bfe gene (88 min) were isolated. Of 20 such lysogens examined, 2 produce lysates with transducing phage containing the metBJF gene cluster (87 min). Reintroduction of the ppc-argECBH chromosome segment (which lies between the bfe and met genes) into these strains virtually abolishes the production of met transducing phage. All of the phage examined have lost essential genes from the left arm of the lambda chromosome. Approximately 85% of the phage appear to have the same genetic composition, containing the metBJF gene cluster, but not the closely linked gene cytR, and having lost phage genes G and J. Analytical CsCl density gradient centrifugation of five representatives of this major class of phage shows four of them to have identical densities (lighter than lambda), while the fifth cannot be resolved from lambda. The four apparently identical phage were isolated from three separate lysates, which suggests the existence of preferred sites for illegitimate recombination on the bacterial and phage chromosomes. Three specialized transducing phage that carry cytR in addition to metB, metJ, and metF have also been studied. Each of these viruses has a different amount of phage deoxyribonucleic acid. Two of them have less deoxyribonucleic acid than lambda, whereas the third has about the same amount. The metB, metF, and cytR genes of the transducing phage have been shown to function in vivo. The phage-borne metB and metF genes are subject to metJ-mediated repression.

A new method for the assay of tissue. S-adenosylhomocysteine and S-adenosylmethione. Effect of pyridoxine deficiency on the metabolism of S-adenosylhomocysteine, S-adenosylmethionine and polyamines in rat liver

The hepatic synthesis and accumulation of S-adenosylhomocysteine, S-adenosylmethionine and polyamines were studied in normal and vitamin B-6-deficient male albino rats. A method involving a single chromatography on a phosphocellulose column was developed for the determination of S-adenosylhomocysteine and S-adenosylmethionine from tissue samples. Feeding the rat with pyridoxine-deficient diet for 3 or 6 weeks resulted in a four- to five-fold increase in the concentration of S-adenosylhomocysteine, whereas that of S-adenosylmethionine was only slighly elevated. The concentration of putrescine was decreased to half, that of spermidine was somewhat decreased and that of spermine remained fairly constant. The activities of L-ornithine decarboxylase, S-adenosyl-L-methionine decarboxylase, L-methionine adenosyltransferase and S-adenosyl-L-homocysteine hydrolase were moderately increased. S-Adenosylmethionine decarboxylase showed no requirement for pyridoxal 5'-phosphate. The major effect of pyridoxine deficiency of S-adenosylmethionine metabolism seems to be a block in the utilization of S-adenosylhomocysteine, resulting in the accumulation of this metabolite to a concentration that may inhibit biological methylation reactions.

A sensitive isotopic assay method for S-adenosylhomocysteine hydrolase. Some properties of the enzyme from rat liver

A rapid and sensitive isotopic method is presented for the assay of S-adenosylhomocysteine hydrolase (EC 3.3.1.1) activity, based on the formation of radioactive S-adenosylhomocysteine labelled in the adenosine portion. The radioactive product is separated either by low-voltage paper electrophoresis or by using phosphocellulose ion-exchange paper. Some kinetic properties of the enzyme from rat liver have shown to be clearly different from those reported earlier for this enzyme. The use of erythro-9-(2-hydroxy-3-nonyl)adenine, a potent inhibitor of adenosine deaminase, makes it possible to measure the S-adenosylhomocysteine hydrolase activity in tissues with a high adenosine deaminase activity, e.g. in intestinal mucosa.

Synthesis of hepatic polyamines, ribonucleic acid and S-adenosylmethionine in normal and oestrogen-treated chicks

1. The hepatic synthesis and accumulation of polyamines, RNA and S-adenosylmethionine were studied in normal and oestrogen-treated immature male chicks. 2. Ornithine decarboxylase activity in chick liver and in whole chick embryo homogenate was preferentially located in the soluble supernatant fraction. 3. In general the activities of the enzymes involved in the synthesis of polyamines and S-adenosylmethionine decreased with increasing age.