Corrigendum

1981 ◽  
Vol 91 (2) ◽  
pp. 365
Keyword(s):  
Specific Activity ◽  
Percentage Change ◽  
Solvent Systems ◽  
Constant Specific Activity

In the paper by Charlotte A. Llewelyn (J. Endocr. 1981, 89, 283–288) the first two sentences of the Results section should read as follows. The area on the initial chromatogram run corresponding to progesterone contained one 14C-labelled peak coincident with carrier progesterone in solvent systems 4, 5 and 6. The area corresponding to androstenedione had the same relative front (RF) value as carrier androstenedione in solvent systems 3, 4 and 6 and was recrystallized to constant specific activity, e.g. after four successive recrystallizations the percentage change in radioactivity per mg was 1·2 ± 1·6 (mean ± s.e.m.).

DEFINITIVE IDENTIFICATION OF MICROQUANTITIES OF RADIOACTIVE STEROIDS BY RECRYSTALLIZATION TO CONSTANT SPECIFIC ACTIVITY

1965 ◽  
Vol 49 (2_Suppl) ◽  
pp. S7-S77 ◽  
Author(s):  
Leonard R. Axelrod ◽  
Charles Matthijssen ◽  
Joseph W. Goldzieher ◽  
Jean E. Pulliam
Keyword(s):  
Liquid Scintillation ◽  
Specific Activity ◽  
Inorganic Materials ◽  
Dual Isotope ◽  
Advantages And Disadvantages ◽  
Yield Values ◽  
Solvent Systems ◽  
Identification Techniques ◽  
Constant Specific Activity

ABSTRACT Studies of steroid metabolism using isotopically-labeled compounds at physiological levels present unique problems in the identification of the metabolites and in the demonstration of their radiochemical purity. The submicrogram quantities of material available preclude the use of classical identification techniques. The character of the evidence obtained, the advantages and disadvantages of chromatographic and countercurrent distribution methods are discussed. Crystallization to constant specific activity is a recognized method for demonstrating that a substance is not radiochemically impure. Its parameters have never been accurately defined. Its true power is achieved only when it is preceded by extensive purification of the material to be characterized. In this way, the unknown material is first categorized by its migration rate in various solvent systems, and then by its crystalline identity with the carrier compound. The likelihood of two dissimilar steroids being both isopolar and isomorphic is held to be remote. Liquid scintillation spectrometry and gravimetry are the techniques used for the determination of constant specific activity. This method for measurement of radioactivity is extremely flexible, sensitive, and lends itself to dual-isotope experiments. Gravimetry under standardized conditions is suitably precise and much more generally applicable than spectroscopic quantitation. The parameters of the technique of rapid, forced microcrystallization are analyzed. In particular, the problem of contamination of crystals is analyzed in detail, and it is pointed out that classical concepts of purification by crystallization, developed chiefly in connection with ionic inorganic materials, must be modified when applied to nonionic steroid compounds. A mathematical analysis of the errors inherent in this technique indicates that 3 successive crystallizations of a pure radioactive compound should yield values for the specific activity which are within ± 5 % of the average of the 3 values.

THE LESS-POLAR METABOLITES PRODUCED BY INCUBATION OF TESTOSTERONE-4-14C WITH RAT AND BOVINE BRAIN

1969 ◽  
Vol 61 (4) ◽  
pp. 641-648 ◽  
Author(s):  
Leon J. Sholiton ◽  
Emile E. Werk
Keyword(s):  
Thin Layer ◽  
Thin Layer Chromatography ◽  
Paper Chromatography ◽  
Specific Activity ◽  
Bovine Brain ◽  
Polar Fraction ◽  
End Products ◽  
Polar Metabolites ◽  
Layer Chromatography ◽  
Constant Specific Activity

ABSTRACT Rat and bovine brain have been incubated with testosterone-4-14C under standard conditions. With use of paper chromatography, the extracted metabolites were noted to fall into less-polar, iso-polar, and more polar fractions. The components of the less-polar fraction were separated by acetylation and thin-layer chromatography and the major end-products identified by recrystallization to constant specific activity or constant 3H/14C ratios. Androst-4-enedione and 5α-dihydrotestosterone were formed consistently under the conditions utilized. Trace amounts of other less-polar metabolites were noted occasionally.

Effects of insulin on glucose turnover rates in vivo: Isotope dilution versus constant specific activity technique

Metabolism ◽  
1996 ◽  
Vol 45 (1) ◽  
pp. 82-91 ◽  
Author(s):  
Ole Hother-Nielsen ◽  
Jan Erik Henriksen ◽  
Jens Juul Holst ◽  
Henning Beck-Nielsen
Keyword(s):  
Isotope Dilution ◽  
Specific Activity ◽  
Glucose Turnover ◽  
Turnover Rates ◽  
Constant Specific Activity

Theory of production rate calculations in steady and non-steady states and its application to glucose metabolism

1992 ◽  
Vol 262 (6) ◽  
pp. E779-E790 ◽  
Author(s):  
J. A. Jacquez
Keyword(s):  
Steady State ◽  
Experimental Design ◽  
Specific Activity ◽  
Glucose Production ◽  
Central Compartment ◽  
Correct Equation ◽  
Endogenous Production ◽  
Correction Terms ◽  
Theory Of Production ◽  
Constant Specific Activity

I present a review and synthesis of the basic theory, steady state, and non-steady state for the calculation of metabolite production rates for systems that have a central well-mixed compartment that is the site of tracer input and sampling. The theory is then applied to the calculation of glucose production. If the only inputs are into the central compartment, an experimental design that involves varying tracer infusion rates to maintain constant specific activity in the central compartment and the same constant specific activity in the peripheral compartments allows calculation of the endogenous production. That holds even if the models are unidentifiable. The correct equation and Steele's pool fraction approximation reduce to the same result for this experimental design. However, that does not justify the use of Steele's equation when there are deviations from the exact experimental design. When the specific activity in the central compartment is not constant, model-dependent correction terms to Steele's equation are needed.

Preparation of 14C- and 3H-Labeled Aflatoxins

1971 ◽  
Vol 54 (5) ◽  
pp. 1027-1031
Author(s):  
J L Ayres ◽  
D J Lee ◽  
R O Sinnhuber
Keyword(s):  
Thin Layer ◽  
Aspergillus Flavus ◽  
Column Chromatography ◽  
Aflatoxin B1 ◽  
Sodium Acetate ◽  
Specific Activity ◽  
Tritiated Water ◽  
New Method ◽  
Extraction And Purification ◽  
Constant Specific Activity

Abstract A new method for the preparation of 14C- and 3H-labeled aflatoxins was devised, using rice as a supporting mold media. Labeled precursors were added to sterile rice and the mixture was inoculated with Aspergillus flavus spores. After a 7 day incubation at 25°C, the toxins were extracted with chloroform and purified by column chromatography and subsequent recrystallization. Aflatoxins B1 and G1 were recovered with 70% efficiency from the culture. Incorporation of radioactivity was examined with glucose-U-14C, sodium acetate-1-14C, and sodium acetate-2-14C. The latter gave the most efficient incorporation of 14C at 0.1% for aflatoxin B1 and 0.05% for aflatoxin G1. Conversion of 3H from tritiated water was 0.006% for aflatoxin B1 and 0.003% for aflatoxin G1. Extensive tests of radiopurity were performed on the labeled toxin which included: recrystallization to constant specific activity, thin layer and column chromatography, and hydrogenation of aflatoxin B1 to tetrahydrodeoxoaflatoxin B1. The rice-culturing technique gave good toxin yields of 1 mg aflatoxin B1/g rice. The purification was simplified by the absence of highly radioactive impurities and no appreciable degradation of labeled toxins was noted throughout extraction and purification.

GLUCOCORTICOID SYNTHESIS FROM PREGNENOLONE BY SHEEP FOETAL ADRENALS IN VITRO

1973 ◽  
Vol 58 (3) ◽  
pp. 485-491 ◽  
Author(s):  
I. J. DAVIES ◽  
K. J. RYAN
Keyword(s):  
Isotope Dilution ◽  
Adrenal Glands ◽  
Specific Activity ◽  
Newborn Period ◽  
Adult Sheep ◽  
Age Related ◽  
Period Of Gestation ◽  
Constant Specific Activity

SUMMARY [7-3H]Pregnenolone was incubated with homogenates of adrenal glands from two 100-day-old sheep foetuses. Cortisol and corticosterone were isolated and identified by reverse isotope dilution and recrystallization to constant specific activity. Together these two compounds accounted for 12% and 17% of the substrate with the two tissue preparations. Other C21 and C19 metabolites which were sought were not present in appreciable quantities. Additional incubations were done with the adrenals of lamb foetuses ranging in age from 110 days of gestation to the immediate newborn period. Glucocorticoidogenic capacity similar to that of the 100-day-old foetuses was demonstrated throughout this period and no age-related change was evident. These results demonstrate that the lamb foetal adrenal has a substantial enzymic capacity for glucocorticoid synthesis throughout at least the last third of gestation. In conjunction with the observations of others, these experiments support the hypothesis that during this period of gestation the lamb foetal adrenal is actively synthesizing glucocorticoids in a manner which is similar to the lamb at term and the adult sheep.

FORMATION OF 17α-HYDROXY-PREGNENOLONE, 17α-HYDROXY-PROGESTERONE AND PROGESTERONE BY HYDATIDIFORM MOLES IN VITRO

1969 ◽  
Vol 61 (1) ◽  
pp. 68-75 ◽  
Author(s):  
Hubertus A. van Leusden ◽  
Maria Siemerink
Keyword(s):  
Urinary Excretion ◽  
Specific Activity ◽  
Full Term ◽  
Hydroxy Progesterone ◽  
Experimental Findings ◽  
Hydatidiform Moles ◽  
Constant Specific Activity

ABSTRACT Vesicles of hydatidiform moles were incubated in the presence of [7α-3H]pregnenolone, After the incubation and extraction of tissues and media, 17α-hydroxy-pregnenolone*, 17α-hydroxy-progesterone and progesterone were identified using a number of TLC systems, followed by crystallization to a constant specific activity. [7α-3H] pregnenolone was not converted to oestrone, 17β-oestradiol and oestriol. The experimental findings indicate that hydatidiform moles, like full term placentas, are deficient in the enzymes necessary to convert C21 to C19 steroids. The production of 17α-hydroxy-progesterone and progesterone in the molar trophoblast in situ may contribute to the considerable urinary excretion of pregnanetriol and pregnanediol in patients with hydatidiform moles.

DEAMINATION OF ADENINE AND RELATED COMPOUNDS AND FORMATION OF DEOXYADENOSINE AND DEOXYINOSINE BY LINGCOD MUSCLE ENZYMES

1964 ◽  
Vol 42 (11) ◽  
pp. 1527-1533 ◽  
Author(s):  
H. L. A. Tarr ◽  
A. G. Comer
Keyword(s):  
Purine Nucleoside Phosphorylase ◽  
Specific Activity ◽  
Purine Nucleoside ◽  
Enzyme Extract ◽  
Muscle Enzymes ◽  
Nucleoside Phosphorylase ◽  
Enzyme Preparations ◽  
Adenylic Acid ◽  
Related Compounds ◽  
Constant Specific Activity

Adenylic acid deaminase was destroyed by heating crude extracts of lingcod muscle to 58 °C, while deamination of adenosine and deoxyadenosine was unaffected. Deoxyadenosine was deaminated about 2300 times as fast as adenine by the enzyme extract. The specific activity of the purine nucleoside phosphorylase with adenine and deoxyribose-1-phosphate as substrates was similar to that of the deoxyadenosine deaminase of the enzyme preparations. It can thus be stated with certainty that adenine is a substrate for the nucleoside phosphorylase, that deoxyadenosine thus formed is promptly deaminated to deoxyinosine, and that deamination of adenine to hypoxanthine plays a negligible role in formation of deoxyinosine. The presence of small amounts of deoxyadenosine in the above reaction was verified by radioactive adenine and isolation of deoxyadenosine of constant specific activity by addition of deoxyadenosine carrier.

Constant specific activity input allows reconstruction of endogenous glucose concentration in non-steady state

1990 ◽  
Vol 258 (6) ◽  
pp. E1037-E1040 ◽  
Author(s):  
C. Cobelli ◽  
G. Toffolo
Keyword(s):  
Steady State ◽  
Glucose Concentration ◽  
Specific Activity ◽  
Radioactive Tracer ◽  
In Vivo Studies ◽  
Constant Infusion ◽  
Glucose Turnover ◽  
Glucose System ◽  
Constant Specific Activity

In vivo studies on the glucose system often require its perturbation by an exogenous input of glucose, whereas glucose turnover is assessed by infusing a glucose tracer. The constant infusion represents the usual format of tracer administration, but it has no clear advantage other than simplicity. Here we propose a different tracer infusion format. It consists of infusing the tracer in parallel with unlabeled glucose so as to maintain a constant specific activity in the infusate. This protocol does not increase experimental complexity and provides new information on the glucose system in non-steady state by allowing reconstruction of the endogenous component of glucose concentration. This reconstruction only requires very general assumptions, such as tracer-tracee indistinguishability and mass conservation; in particular it is independent of the glucose model structure, i.e., number of compartments and their interconnections. A proof of the result is given for a general nonlinear model of the glucose system. The constant specific activity input is also advantageous for non-steady-state calculations, because it reduces the variation in the measured plasma glucose specific activity. The glucose system has served as the prototype, but the protocol is applicable to other blood-borne substances. The radioactive tracer case has been considered, but the same results apply to stable isotope tracers as well; in this case they also become relevant in a somewhat different context, i.e., kinetic studies in steady state.

Sign in / Sign up

Export Citation Format

Share Document