Measurement Near Threshold of 9-Be(3-He, Pi) to the A = 12 Isobaric Triplet by Recoil Detection

This work was supported by the National Science Foundation Grant NSF PHY 81-14339 and by Indiana Universit

\u3b2 Oxidative cleavage of octanoyl and dodecanoyl CoA in rat liver cytoplasm

[12 14C] Dodecanoyl CoA and [8 14C] octanoyl CoA were tested as substrates for shortening the chain by two carbon atoms using both the 105,000 x g soluble fraction and the sonicated mitochondrial fraction of rat liver homogenate as the enzyme source. Both substrates were metabolized by the cytoplasmic enzymes giving rise to the accumulation of intermediates of the \u3b2 oxidation process without formation of two carbon units from the methyl carbon of the acyl residue. A new method is described which allows quantitative estimation of volatile fatty acids formed by \u3b2 oxidation of dodecanoyl and octanoyl Coenzyme A

MODULATION OF HMG-COA REDUCTASE-ACTIVITY BY PANTETHEINE PANTETHINE

The ability of pantetheine/pantethine to modulate the aptivity of HMG-CoA reductase (EC 1.1.1.3) was determined in vitro with rat liver microsomes. The decay of the activity was obtained with pantethine in the 10(ex-5)-10(ex-4) M range, whereas stimulation by panlgtheine occurred at 10(ex-3)-10(ex-2) M, as previously reported for GSSG and GSH, respectively. Inhibition of HMG-CoA by pantethine in isolated liver cells was also investigated by measuring the enzyme activity in microsomes isolated from hepatocytes incubated without or with 1 mM pantethine under conditions previously shown by us to induce inhibition of cholesterol synthesis from acetate. The enzyme amount was not modified by pantethine, but in cells treated with the disulphide, the relative amounts of the thiolic active forms of the enzyme, both phosphorylated and dephosphorylated, were decreased to about half compared to controls

EVIDENCE FOR A DIFFERENT METABOLIC BEHAVIOR OF CYTIDINE DIPHOSPHATE CHOLINE AFTER ORAL AND INTRAVENOUS ADMINISTRATION TO RATS

Radioactivity plasma decay was studied in rats after intravenous and oral administration of cytidine diphosphate [methyl-l4c] choline at doses of 25 and 300 mg,/kg. The kinetics fitted well with a two compartment open model and showed a long Lasting elimination phase with a half-life ranging from 2.0 to 2.6 days for the two doses and the two administration routes. Absorption of cytidine diphosphate choline radioactivity was complete after oral treatment with the 1ow dose and accounted for 94.5 % of the dose when 300 mg/kg of cytidine diphosphate [methyl-14c] choline were administered. However the distribution of radioactivity in tissues, urine and expired air suggest metabolic differences, at least from a quantitative point of view, between the oral and intravenous treatments. In particular, the higher excretjon of radioactivity associated with trimethylamine in urine found when cytidine diphosphate [methyl-l4C]choline was given orally, suggest that the compound may be metabolized, at least in part, previous to its gastrointestinal absorption

LACK OF CONVERSION OF XANTHINE DEHYDROGENASE TO XANTHINE-OXIDASE DURING WARM RENAL ISCHEMIA

Irreversible transformation of xanthine dehydrogenase (XDH) to xanthine oxidase (XO) during ischemia was determined measuring XDH and total enzyme activity in kidneys before and after 60 min ofclamp ofthe renal pedicle. Tissue levels ofadenine nucleotides, xanthine and hypoxanthine were used as indicators of ischemia. After 60 min of clamping, ATP levels decreased by 72/. with respect to controls whereas xanthine and hypoxanthine progressively reached tissue concentrations of 732+49 and 979+ l5 nmol'g tissue 1, respectively. Both total and XDH activities in ischemic kidneys (30+ 15 and l9* I nmol'min I'g tissue-r) were significantly lower than in controls when expressed on a tissue weight basis. The fraction of enzyme in the XDH form was however unchanged indicating that the reduction of the nucleotide pool is not accompanied by induction ofthe type-O activity ofxanthine oxidase

DETERMINATION OF SERUM GLUCOSE BY ISOTOPE-DILUTION MASS-SPECTROMETRY - CANDIDATE DEFINITIVE METHOD

We report a rather simple method to determine glucose concentration in serum, using isotope dilution mass spectrometry and [C-13(6)]glucose as internal standard. The procedure involves a single step of sample purification and the conversion of the analyte into its aldononitrile pentaacetate. The between-day and within-day contribution to total variance for a single measurement was determined by assaying Standard Reference Material (SRM) 909 serum. The method was then applied to measurement of glucose concentration in three lyophilized sera: SRM 909 and two other commercially available sera. In the two studies, the concentration of SRM 909 serum was found to be 0.8% above and 0.3% below the reported value (6.25 mmol/L), respectively; the overall coefficient of variation for determinations in all sera ranged from 0.37% to 0.56%. The precision and the accuracy of the method satisfy the requirements for a Definitive Method

ENZYMATIC-SYNTHESIS OF [METHYL-(H-2)3] CREATININE

2-Amino-1,5-dihydro-1-[methyl-H-2(3)] 4H-imidazol-4-one ([methyl-H-2(3)] creatinine) was obtained by acidification and heating (120-degrees-C, 120 min) of the [methyl -H-2(3)] N-amidinosarcosine (creatine) synthesised by methylation of guanidoacetate (GA) with S-adenosyl-[methyl-H-2(3)) L-methionine ([methyl-H-2(3)] AdoMet) in the presence of rat liver guanidoacetate methyltransferase (GAA-MT). Isotopic enrichment was 94.7 %