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M Yudkoff

Publications and source records attributed to M Yudkoff.

At least 91 records · Page 5Linked to original sources
PubMed1987

Albumin synthesis in premature infants: determination of turnover with [15N]glycine.

Albumin turnover was studied in seven small premature infants who received a constant infusion of [15N]glycine for 60-72 h. Gas chromatography-mass spectrometry was used to measure the rate of appearance of [15N]glycine in albumin isolated from the blood. By comparing the linear increment of [15N]glycine in blood albumin with plateau labelling of urinary [15N]hippurate, which was assumed to reflect intrahepatic isotopic abundance in [15N]glycine, the fractional synthetic rate for albumin was found to be 0.09-0.177 day-1 (mean +/- SD = 0.122 +/- 0.041 day-1). The absolute synthesis rate for albumin was 0.3 +/- 0.099 g/dl plasma X day-1 and the total plasma synthetic rate was 117.6 +/- 37.0 mg/kg X day-1. The glycine flux was 326.0-927.7 mumol/kg X h-1 (mean +/- SD 516.7 +/- 218.4 mumol/kg hr-1). The percentage of the glycine flux incorporated into albumin in the total vasculature was 0.425 +/- 0.344. The fractional synthetic rate and the absolute synthetic rate for albumin in these small premature infants are much higher than values obtained in healthy young adults studied with a similar methodology. The relatively low serum albumin concentrations typical of premature infants appear to be referable to more rapid turnover of a small plasma pool rather than a diminution in the rate of albumin synthesis.

Gas Chromatography-Mass Spectrometry↗
PubMed1986

Effect of 5-amino-4-imidazolecarboxamide riboside on renal ammoniagenesis. Study with [15N]aspartate.

[15N]Aspartate and 5-amino-4-imidazolecarboxamide riboside (AICAriboside) were used to evaluate the contribution of the purine nucleotide cycle to ammonia production in renal tubules isolated from control and chronically acidotic rats. Addition of 1 mM AICAriboside to incubation medium containing 2.5 mM [15N] aspartate significantly stimulated production of 15NH3 and 15N in the 6-amino group of adenine nucleotides during a 30-min incubation. In tubules from both control and acidotic animals, the levels of ATP, AMP, and NH3 were increased. In contrast, 5 mM AICAriboside inhibited 15NH3 production and reduced the total purine nucleotide content. In tubules from acidotic rats, enrichment in 15NH3 exceeded that in the 6-amino group of the adenine nucleotides, indicating that no precursor-product relationship existed between the purine nucleotide cycle and ammonia. Conversely, in tubules from control rats, 15N enrichment in the 6-amino group of the adenine nucleotides exceeded that in NH3. This relationship obtained whether or not AICAriboside was included in the incubation mixture. The current investigations show that the metabolism of aspartate through the purine nucleotide cycle is lower in renal tubules obtained from chronically acidotic rats than in control tubules. The observations indicate that AICAriboside has a biphasic effect on renal ammoniagenesis and adenine nucleotide synthesis, and suggest a possible clinical use of AICAriboside in cases of impaired ammonia formation in renal failure.

Adenosine Diphosphate↗
PubMed1986

Utilization of [15N]glutamate by cultured astrocytes.

The metabolism of 0.25 mM-[15N]glutamic acid in cultured astrocytes was studied with gas chromatography-mass spectrometry. Almost all 15N was found as [2-15N]glutamine, [2-15N]glutamine, [5-15N]glutamine and [15N]alanine after 210 min of incubation. Some incorporation of 15N into aspartate and the 6-amino position of the adenine nucleotides also was observed, the latter reflecting activity of the purine nucleotide cycle. After the addition of [15N]glutamate the ammonia concentration in the medium declined, but the intracellular ATP concentration was unchanged despite concomitant ATP consumption in the glutamine synthetase reaction. Some potential sources of glutamate nitrogen were identified by incubating the astrocytes for 24 h with [5-15N]glutamine, [2-15N]glutamine or [15N]alanine. Significant labelling of glutamate was noted with addition of glutamine labelled on either the amino or the amide moiety, reflecting both glutaminase activity and reductive amination of 2-oxoglutarate in the glutamate dehydrogenase reaction. Alanine nitrogen also is an important source of glutamate nitrogen in this system.

Adenosine Triphosphate↗
PubMed1986

Nitrogen sources for renal ammoniagenesis: study with 15N amino acid.

The contribution of amino acids other than glutamine to renal ammoniagenesis was investigated in renal tubules obtained from control rats and rats with metabolic acidosis by incubating 2.5 mM [5-15N]glutamine, [2-15N]glutamine, [15N]glutamate, [15N]aspartate, [15N]alanine, or [15N]glycine, either as the sole N source in Krebs bicarbonate buffer or as a labeled substrate in a medium containing a mixture of unlabeled amino acids. With control tissue in Krebs buffer, approximately 75% of total ammonia was derived from 5-N of glutamine, whereas 2-N of glutamine, glutamate, aspartate, alanine, and glycine supplied 1, 10, 13, 4, and 18%, respectively. In the acidotic state, these values were 51, 30, 30, 30, 10, and 15% of the total ammonia produced, respectively. The ammonia that could not be accounted for by 15N analysis was derived from endogenous sources. Studies with tubules incubated in Krebs medium alone indicated that, in both control and acidosis, the calculated fraction of ammonia derived from endogenous sources was significantly decreased by addition of either 0.7 or 2.5 mM glutamine. However, ammonia production from endogenous sources was similar whether 0.7 or 2.5 mM glutamine was used as a sole exogenous substrate. Incubations of control tissue in buffer supplemented with an amino acid mixture revealed a significant decrease in ammonia production from [5-15N]glutamine compared with incubation in Krebs buffer alone. In chronic acidosis, no significant difference was found in total ammonia formation from [5-15N]glutamine compared with Krebs buffer alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Acidosis↗
PubMed1986

Methods for determining the protein requirement of infants.

Although there is no clearly preferred method to determine the precise protein requirement of infants, a variety of techniques have been employed to provide a reasonable approximation of this variable. These approaches include anthropometric measurements, the determination of nitrogen balance, the estimation of rate of whole body protein synthesis and catabolism by the administration of amino acids labeled with stable isotopes, and the determination of serum concentrations of certain proteins and amino acids.

Amino Acids↗
PubMed1986

Direct measurement of apolipoprotein B synthesis in human very low density lipoprotein using stable isotopes and mass spectrometry.

Stable isotope methodology has been adapted to the study of lipoprotein turnover in human subjects. Using endogenous [15N]glycine labeling and gas-liquid chromatographic-mass spectrometric analysis, synthesis of apolipoprotein B in very low density lipoprotein (VLDL) was measured directly in five normal and two hyperlipidemic subjects. An isotopic precursor steady state was achieved during the studies by utilizing a priming dose and constant infusion containing [15N]glycine. Measurement of the plateau in 15N enrichment in the urinary hippurate produced during each study was used to estimate the 15N enrichment of the hepatic glycine precursor pool. The range of values for the fractional synthetic rate of VLDL apoB in the normal subjects obtained by this method was 5.9 to 11.5 day-1, with a mean of 9.2 +/- 2.4 (SD). This value agrees with the results of previous investigations which have utilized other methods. The method was also tested in two hypertriglyceridemic subjects and gave fractional synthetic rates of VLDL apoB that were significantly lower than in normals (1.5 and 2.8 day-1). This stable isotope method allows calculation of the fractional synthetic rate of VLDL apoB by maintaining an isotopic steady state throughout the study. It makes possible repeated studies in the same individual since no risk of exposure to radioisotopes is involved.

Apolipoproteins B↗
PubMed1985

Metabolism of glutamine and glutamate by rat renal tubules. Study with 15N and gas chromatography-mass spectrometry.

Gas chromatography-mass spectrometry was utilized to study the metabolism of [15N]glutamate, [2-15N]glutamine, and [5-15N]glutamine in isolated renal tubules prepared from control and chronically acidotic rats. The main purpose was to determine the nitrogen sources utilized by the kidney in various acid-base states for ammoniagenesis. Incubations were performed in the presence of 2.5 mM 15N-labeled glutamine or glutamate. Experiments with [5-15N]glutamine showed that in control animals approximately 90% of ammonia nitrogen was derived from 5-N of glutamine versus 60% in renal tubules from acidotic rats. Experiments with [2-15N]glutamine or [15N]glutamate indicated that in chronic acidosis approximately 30% of ammonia nitrogen was derived either from 2-N of glutamine or glutamate-N by the activity of glutamate dehydrogenase. Flux through glutamate dehydrogenase was 6-fold higher in chronic acidosis versus control. No 15NH3 could be detected in renal tubules from control rats when [2-15N]glutamine was the substrate. The rates of 15N transfer to other amino acids and to the 6-amino groups of the adenine nucleotides were significantly higher in normal renal tubules versus those from chronically acidotic rats. In tubules from chronically acidotic rats, 15N abundance in 15NH3 and the rate of 15NH3 appearance were significantly higher than that of either the 6-amino group of adenine nucleotides or the 15N-amino acids studied. The data indicate that glutamate dehydrogenase activity rather than glutamate transamination is primarily responsible for augmented ammoniagenesis in chronic acidosis. The contribution of the purine nucleotide cycle to ammonia formation appears to be unimportant in renal tubules from chronically acidotic rats.

Acid-Base Equilibrium↗
PubMed1985

Gas chromatographic-mass spectrometric determination of isotopic enrichment of 6-15NH2 in adenine nucleotides.

A gas chromatographic-mass spectrometric method for the determination of isotopic abundance in [6-15NH2]adenine nucleotides is described. The method involves formation of the di-t-butyldimethylsilyl (TBDMS) derivative of adenine following isolation of the nucleotide fraction with solid-phase ion-exchange chromatography and subsequent acid hydrolysis of nucleotides to free base. Mass spectra for both adenine-diTBDMS and [6-15NH2]adenine-diTBDMS were obtained to identify those ions containing the 6-NH2 moiety. The base peak (m/z 306) was formed by loss of C4H9 (57) and constitutes approximately one-third of the total ion current. Using selected ion monitoring of the m/z 306/m/z 307 ratio, levels of isotopic abundance of 1.0-50.0 mol% excess could be measured reproducibly with the injection of 10-20 pmol of the adenine-diTBDMS derivative obtained from isolated rat hepatocytes. Confirmation that measured isotopic abundance was referable to labeling of the 6-15NH2 group was obtained by oxidation of adenine to hypoxanthine and determination of enrichment in the hypoxanthine-diTBDMS derivative. The method was used to study the formation of [6-15NH2]adenine nucleotides during the incubation of isolated rat hepatocytes with [15N]alanine. A level of approximately 6.0 mol% excess was observed at 60 min incubation.

Adenine↗
PubMed1985

Metabolic and mitochondrial morphological changes that mimic Reye syndrome after endotoxin administration to rats.

The administration of sublethal doses of Escherichia coli O111:B4 endotoxin to starved rats results in significant increases in plasma ammonia, free fatty acids, and serum lactate compared with starved controls. These metabolic alterations are associated with Reye syndrome-like histological findings of hepatic microvesicular fatty accumulation and hepatic ultrastructural evidence of mitochondrial pleomorphism with matrix disruption. This sublethal endotoxin model may help elucidate the relationship between the hepatic mitochondrial injury, characteristic metabolic impairment, and encephalopathy seen in patients with Reye syndrome.

Alanine Transaminase↗
PubMed1984

Simultaneous determination of [2-15N]- and [5-15N]glutamine with gas chromatography-mass spectroscopy: applications to nitrogen metabolic studies.

A gas chromatographic-mass spectrometric method for analysis of L-[2-15N]- and L-[5-15N]glutamine is described. The method is based on direct acylation of glutamine with trifluoroacetic anhydride and the formation of the N,N-bis-trifluoroacetyl-L-glutamine derivative. This simple and sensitive method is capable of detecting approximately 0.5 atom% excess 15N in as little as 10 microliter of plasma with a mean coefficient of variance of 11.6%. The method was applied to determine the appearance of 15N enrichment in plasma amino-N and amide-N of glutamine in a healthy adult volunteer during a constant infusion of 15NH4Cl. A plateau level of 3.7 and 2.6 atom% excess was observed in amide-N and amino-N, respectively, at 1 and 2 h after 15NH4Cl infusion was started.

Acetic Anhydrides↗
PubMed1984

Urinary excretion of dimethylarginines in premature infants.

Urinary excretion of NG,N'G-dimethylarginine (NG,N'G-Me2Arg) and NG,NG-dimethylarginine (NG,NG-Me2Arg) was measured in premature infants. The NG,N'G-Me2Arg/NG,NG-Me2Arg ratio was much higher in newborn infants than in older children or adults. Linear regression analysis showed a significant negative correlation between the degree of maturity and the excretion of NG,N'G-Me2Arg. A significant direct linear relationship also was found between the excretion of NG,N'G-Me2Arg and the rate of whole body nitrogen flux and of protein synthesis and catabolism. No correlation was found between the excretion of the dimethylarginines and 3-methylhistidine, but the dimethylarginine/3-methylhistidine ratio declined with advancing conceptual age. A direct linear relationship was found between excretion of NG,N'G-Me2Arg and NG,NG-Me2Arg and whole body nonskeletal muscle protein breakdown. No correlation was found between nonskeletal muscle protein catabolism and 3-methylhistidine excretion. We estimate that approximately 0.34 mumole of dimethylarginine are excreted per gram of nonskeletal muscle protein catabolized. Dietary intake did not affect the excretion of either NG,N'G-Me2Arg or NG,NG-Me2Arg. The data suggest that measurement of urinary dimethylarginines might be useful in the nutritional assessment of premature infants.

Adolescent↗
PubMed1984

Whole body nitrogen kinetics in man: determination from plasma [guanidino-15N]arginine.

Whole body nitrogen turnover and protein synthesis were calculated by the method of D. Picou & T. Taylor-Roberts [Clinical Science and Molecular Medicine (1969) 36, 283-296] except that plateau plasma enrichment of [guanidino-15N]arginine was used in place of the [15N]urea enrichment after a constant infusion of [15N]-glycine. With this approach metabolic pool turnover and protein synthesis were 637.2 +/- 73.0 mg of N day-1 kg-1 and 2964.0 +/- 409.5 mg of protein day-1 kg-1 respectively. Virtually identical isotopic enrichment in [guanidino-15N]arginine and [15N]urea were observed in a healthy young adult who took repeated oral doses of [15N]glycine for a period of 60 h: 0.47 (arginine) and 0.48 (urea) atom% excess. The turnover of glycine nitrogen and of urea, determined from the constant infusion of [15N]glycine and [13C]urea, was 66.2 +/- 3.3 mg of N day-1 kg-1 and 156.2 +/- 4.3 mg of urea day-1 kg-1 respectively. The ratio of steady-state enrichment in arginine to that in glycine, reflecting the fraction of arginine derived from glycine, was 10.5%. By using the [guanidino-15N]arginine enrichment as representative of the expected enrichment in [15N]urea at plateau, it was calculated that approximately 25% of glycine N flux is directed toward the synthesis of urea, with the remainder directed to protein and quantitatively minor products like haem and creatinine.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1984

Metabolism of 15NH3 in organotypic cerebellar explants and cultured astrocytes: studies with gas chromatography-mass spectrometry.

Gas chromatography-mass spectrometry was used to study the metabolism of 15NH3 in organotypic cerebellar explants and cultured astrocyte monolayers. A steady-state level of 15NH3 was present by 1 min in both systems. Steady-state labeling in L-[amide-15N] glutamine, L-[15N]alanine, L-[15N]glutamate, and L-[15N]aspartate was attained by 1 min after 15NH3 addition in the organotypic cerebellar explants and by approximately 5 min in the cultured astrocytes. No measurable 15N labeling was noted in either glycine or serine in either system.

Ammonia↗
PubMed1984

Glycogen storage disease: effects of glucose infusions on [15N]glycine kinetics and nitrogen metabolism.

The effects of intragastric glucose infusions on [15N]glycine kinetics and whole body protein turnover were investigated in four children with type I and two children with type III glycogen storage disease. Either fasting or the administration of insufficient glucose was associated with a diminution in the glycine pool size relative to values observed when patients received adequate glucose. The cause of the smaller pool size was an increased fractional glycine turnover. Simultaneous determination of whole body protein turnover, using a stochastic model based on [15N]urea excretion, showed higher rates of protein synthesis, nitrogen flux, net tissue protein retention, and reutilization of amino acid nitrogen derived from protein catabolism, in patients receiving sufficient exogenous glucose. Depletion of amino acid pools, presumably because of intensive utilization of these gluconeogenic precursors when inadequate glucose is administered, was associated with a lower rate of whole body protein synthesis.

Adolescent↗
PubMed1983

[15N] leucine as a source of [15N] glutamate in organotypic cerebellar explants.

Approximately 26.0% of the [15N] glutamate and [alpha 15N] glutamine formed in organotypic cerebellar explants was derived from [15N] leucine. Approximately 14.0% of the 15NH3 and [amide 15N] glutamine synthesized came from leucine nitrogen. Another 4.0% of the alpha nitrogen of both glutamate and glutamine was derived from [15N] valine. These results suggest that branched-chain amino acids, particularly leucine, may be important for the synthesis of glutamic acid by the brain.

Amino Acids↗
PubMed1983

Rapid determination of [guanidino-15N]arginine in plasma with gas chromatography--mass spectrometry: application to human metabolic studies.

A rapid gas chromatographic-mass spectrometric method for the determination of 15N in the guanidino nitrogens of arginine is described. The method is based on formation of the N-tetratrifluoroacetyl-arginine derivative. Approximately 0.15 mol% excess 15N can be detected in as little as 50 microliters of plasma with an average coefficient of variation of 8.8%. The possible fragmentation pattern of the N-tetra-trifluoroacetyl-arginine derivative is described. The method was applied to determine the appearance of 15N enrichment in plasma arginine in a healthy adult volunteer during a constant infusion of 15NH4Cl. A plateau level of 0.7 atom% excess was observed 2 h after the 15NH4Cl infusion was started.

Acetic Anhydrides↗
PubMed1983

A model for determination of total body protein synthesis based upon compartmental analysis of the plasma [15N] glycine decay curve.

A model for whole body glycine nitrogen flux based on the compartmental analysis of plasma [15N] glycine decay curves is described and used for the measurements of (1) total body glycine nitrogen flux and the components of this flux in three healthy young adults and (2) total body protein synthesis based on the conversion of 15N to excretory products, ie, the sum of urinary [15N] urea and 15NH3 and the amount of labeled urea remaining in the body at five hours following administration of [15N] glycine. The mean glycine nitrogen flux was 3.93 +/- 0.42 mg N X kg-1 X h-1 (SEM). The major components of this flux are de novo synthesis of glycine, which accounts for 18% to 27%, and release from protein breakdown, which accounts for 62% to 73%. The outward pathways of glycine from the total body free glycine pool are conversion to other amino acids and oxidation to excretory end products (30% to 42%) and incorporation into protein, which accounts for 45% to 61% of glycine N loss from the metabolic pool. The mean rate of total body protein synthesis as determined by compartmental analysis was 3.56 g protein X kg-1 X day-1. The results that were obtained for protein synthesis and whole body glycine kinetics accord well with previous studies in normal adults, using the stochastic model.

Adult↗