Uptake of radioactive carbon

The range of this method depends very largely on the amount of radioactive carbon added and the precision of the radiochemical part of the procedure. There is virtually no upper limit and the lower limit could probably be reduced to 0.01 mg C/m per hr by using great care. An absolute lower value will exist, however, depending upon the reproducibility of dark blanks see later). The above range is a realistic one under routine conditions. 

A known amount of radioactive carbonate, COj , is added to sea water of known total carbonate content. (The addition of inactive carbonate with the labelled material is negligible.) After photosynthesis by the endemic phytoplankton population has continued for a suitable period the cells are filtered onto a membrane filter, washed and dried, and the radioactivity from the carbon in the plants is measured with a suitable Geiger counter. This uptake of radioactive carbonate, as a fraction of the whole, is assumed to measure the uptake of total carbonate, as a fraction of the whole, and hence the rate of photosynthesis may be evaluated. 

BOD bottles (clear and opaque) cleaned, etc. as described in Part V.2, Section C. 

The 25-mm diam Millipore filtration apparatus should be fitted with a funnel to hold more than 300 ml of liquid. A manostat device (there are several cheap commercial laboratory models based on the Cartesian diver) set to regulate the suction to the filtration unit to prevent the vacuum becoming greater than 150-200 mm of mercury. 

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The method builds on the fundamentals of radiocarbon dating via analysis, an analytical method that relies on the nuclear decay of radioactive carbon that is incorporated from the atmosphere into all living, respiring plants. The is present in the atmosphere as " C02. The level of is extremely low, only one part per trillion of the natural abundance of carbon in the atmosphere. When plant respiration ceases, the uptake of stops, but the slow radioactive decay of... 

The study reported in Table 4.12 illustrates the role of carnitine in fatty add oxidation and introduces the topic of medium-chain fatty acids. This study, conducted before the role of carnitine in fatty acid transport was realized, involved addition of radioactive fatly acids to suspensions of liver mitochondria. The fatty acids used iriduded [ "Cjoctanoic acid (medium-chain) and [ " Clpalmitic add (long-chain). The susperisions were incubated for 30 minutes to permit uptake of the fatty acids, their subsequent oxidation, and discharge of radioactive carbon dioxide. The produced in the Krebs cycle diffuses out of the mitochondria into the surrounding fluid-... 

The carbon-14, along with the more abundant carbon-12, is converted into living plant material by the process of photos)mthesis. Carbon proceeds up the food chain as the plants are consumed by animals, including humans. When a plant or animal dies, the uptake of both carbon-14 and carbon-12 ceases. However, the amount of carbon-14 slowly decreases because carbon-14 is radioactive (fj/j = 5730 years). Carbon-14 decay produces nitrogen ... 

The following method, using a B a-requiring diatom and measuring the rate of radioactive carbonate uptake of cells exposed to different concentrations of the vitamin, is probably the most sensitive and rapid procedure yet available. It is derived from an initial radiocarbon uptake technique by Gold as modified by Carlucci and Silbemagel (Canadian J. Microbiol., 12 175, 1966). 

Kirsch and Korshalla (1964) attempted to relate the significance of methionine as a methyl donor in mitomycin A synthesis by studying the incorporation of radioactive methyl carbon into mitomycin A. The addition of methyl C-methionine to synthetic medium at the start of the fermentation resulted in uptake of radioactivity and its incorporation into the mitomycin. The study undertaken by the above investigators was confined to mitomycin A since it contains two methoxy substitutients at positions 7 and 9 a and is relatively easy to separate and purify in microgram quantities from a mixture of the mitomycins. Evidence was obtained which indicate that all of the radioactivity residing in mitomycin A was equally distributed between the two methoxy functions (Kirsch and Korshalla, 1964). The technique used to determine positional labeling was described in the reference cited above and is based on reaction conditions reported by Webb et al. (1962). 

The possible contribution of this pathway to phytanic acid synthesis in Refsum s disease was investigated in a Norwegian patient who was given 25 juc mevadonic acid-2- " C intravenously. Although there was normal uptake of radioactivity into plasma cholesterol there was little radioactivity in the plasma fatty acids, suggesting that if any biosynthesis of phytanic acid occurred, it must be at a very slow rate. Confirmation was provided by extended studies of the uptake of deuterium oxide over four months in the s lme patient. Although after this time 91% of the expected equilibration occurred between body water and cholesterol, there was minimal incorporation of deuterium in the phytanic acid, and this occurred unevenly, mainly concentrated in the first three carbon atoms of the molecule [121, 126, 127, 128]. 

The uptake of cocaine to hair after preliminary exposure to various acidic and basic solutions is shown in Figure 10. Three sets of experiments were performed. In the first experiment, hair was exposed to base (0.1 M sodium carbonate, pH 12) for 3 h and then washed extensively with water rmtil the water was neutral. This was then followed by two phosphate buffer rinses at pH 5.3 for 10-min periods. The hair was then exposed to 5 pg/mL of cocaine, containing a radioactive tracer, in phosphate buffer at pH 5.3 for 1 h. After exposure the excess cocaine was removed with three water rinses of 10 min each and the hair was dried. Then the hair was decontaminated with ethanol and six phosphate washes, digested, and the cocaine concentration determined by scintillation counting as per previously described procedures. Approximately twice as much cocaine was incorporated into the hair pretreated by exposure to base as compared to hair not subjected to any pretreatment. In the second experiment, hair was pretreated with 0.1 M HCl, then treated as in the first experiment. In this case approximately one sixth as much cocaine was incorporated as the control. In the third experiment, hair was pretreated with 5% acetic add and treated as in the... 

The metabolism of cocaine was inhibited by SKF-525A, a microsomal enzyme inhibitor. The relationship between the pharmacological activity of cocaine and its derivatives and the inhibitory action on uptake of dopamine into striatal synaptosomes has been studied. [N- " CHsjcocaine was metabolized in healthy humans the production of labelled carbon dioxide provided a measure of N-demethylation, which proved to be greater with lower plasma cholinesterase activity. Radioactivity excreted in the urine was 65-75% in 28 hours, and ecgonine methyl ester proved to be the major metabolite (32-49% of urinary metabolites). 

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