Carbohydrates radioactivity

Even higher organisms can be used for the production of labeled compounds. Plants, tobacco, or Canna indica for example, when grown in an exclusive atmosphere of radioactive carbon dioxide, [ 002], utilize the labeled precursor as the sole source of carbon for photosynthesis. After a suitable period of growth, almost every carbon atom in the plant is radioactive. Thus, plants can serve as an available source of C-labeled carbohydrates (9). 

One of the first chemical applications of radioactive tracers was a set of elegant experiments on photosynthesis performed in the 1950s by Melvin Calvin. His goal was to determine the set of reactions used by plants to transform atmospheric CO2 into carbohydrates. Calvin supplied growing plant cells with CO2 enriched with 14... 

The application of substrates isotopically labeled in specific positions makes it possible to follow the fate of individual atoms during the microbial degradation of xenobiotics. Under optimal conditions, both the kinetics of the degradation, and the formation of metabolites may be followed— ideally when samples of the labeled metabolites are available. Many of the classical studies on the microbial metabolism of carbohydrates, carboxylic acids, and amino acids used radioactive... 

Ideally, molecules should be labelled by introducing a radioactive isotope in place of a normal atom, e.g. carbon-14 replacing a carbon-12 in a carbohydrate. This method of labelling involves the synthesis of the molecule either in vivo or in vitro and the use of enzymes often permits the isotope to be introduced in a particular position in the molecule. The position of the labelled atom should be indicated wherever possible as for example in glucose- 1-14C. 

It is difficult to reconcile the unique chemical structure of tetrodotoxin with that of an animal product. Its structure is not related to that of other animal products by any readily recognized biosynthetic scheme. It is not a terpenoid, not obviously formed from amino acid or carbohydrate units, and apparently not constructed from acetate or propionate units. Nor does it resemble any of the various plant alkaloid patterns. It thus appears to be a very unlikely animal product to result from known biogenetic pathways. In this connection the metabolic incorporation of radioactive precursors using torosa and ]C. granulosa salamanders was studied by Shimizu et al. (47). They observed significant isotopic incorporation into amino acids and steroid metabolites, but they found no such incorporation associated with tetrodotoxin. 

Phenylalanine Ammonia-Lyase. The building units of lignin are formed from carbohydrate via the shikimic acid pathway to give aromatic amino acids. Once the aromatic amino acids are formed, a key enzyme for the control of lignin precursor synthesis is phenylalanine ammonia-lyase (PAL) (1). This enzyme catalyzes the production of cinnamic acid from phenylalanine. It is very active in those tissues of the plant that become lignified and it is also a central enzyme for the production of other phenylpropanoid-derived compounds such as flavonoids and coumarins, which can occur in many parts of the plant and in many different organs (35). Radioactive phenylalanine and cinnamic acid are directly incorporated into lignin in vascular tissue (36). 

As shown in Table III, there is no significant difference in glucose uptake by cotton leaf discs immediately after exposure, but after 24 hr the uptake has nearly doubled. The percentage distribution of radioactivity in various extraction fractions is approximately the same in control and ozone-treated tissues. CO2 evolution from the added glucose is virtually identical in control and treated tissues. Isotope incorporation into the water soluble fraction, which would include amino acids, organic acids, and soluble carbohydrate, is also quite similar. Some distributional differences in the insoluble fraction are noted between... 

Measurements of the quantities of glycolipids inserted into the membrane have also been reported by a technique based on the use of C-labeled lipid anchors. In this method, the carbohydrate (a-o-Man) was covalently coupled to the anchor at the surface of a pre-formed vesicle. Indeed, the liposome structure was shown to remain intact in the treatment. Nevertheless, the measurement of the incorporated mannose was performed after separation of bound and unbound material by centrifugation. The yields of coupling were shown to increase with the increase of the initial mannose/ C-anchor ratio, but non covalent insertions were displayed at high initial mannose concentrations. Therefore, the aforementioned method was not as accurate as could have been expected for the use of radioactive materials [142]. Radiolabeled phospholipids were also used for such determinations thus the amounts of glycosphingolipids incorporated into liposomes were quantified by the use of H-phospholipids whereas the amounts of glycolipids were determined by a sphingosine assay [143]. 

Making use of the binding of radioactively labeled specific toxins to identify diem, the subunits of the sodium channel proteins were purified from several sources including die electrical tissue of the electric eel Electrophorus electricus,i37 i39 heart and skeletal muscle, and brain.440-44113 In all cases a large 260-kDa glycoprotein, which may be 30% carbohydrate, is present. The saxitoxin-binding protein from rat brain has two additional 33-36 kDa subunits witii a stoichiometry of a(31P2- The Electrophorus a subunit consists of 1820 residues,437 while rat brain contains a proteins of 2009... 

Sections of non-photosynthetic oat-tissue fed with radioactive substrates (acetate and sucrose) incorporated the label into the soluble carbohydrates and lipides, with no apparent differences between auxin-treated segments and untreated controls. 7 The tissue was apparently grown with an inadequate substrate of carbohydrate, which may explain why indole-3-acetic acid at 1 mg. per liter increased the utilization of sucrose, lipides, and organic acids by pea-stem segments in other work. None of the available investigations on cellular carbohydrates have provided very much promising information concerning the nature of the metabolic functions directly affected by the auxins. 

The rapid, carbohydrate dependent clearance of specifically modified serum glycoproteins, observed in mammalian species (1), was not demonstrable in fish. Of the five proteins examined in Fig. 1, no significantly increased rate of disappearance from the circulation could be correlated with the nature of the terminal, non-reducing glycoside moiety. The marginally faster clearance observed in the case of asialo-orosomucoid, although reproducible, could not be ascribed to the participation of a specific hepatic receptor. This conclusion is supported by the data in Table 1 whereby it is evident that there was no selective accumulation of radioactivity in the liver the major portion of counts recoverable 25 minutes after inj ection were located in the kidneys. 

During World War II, Isbell worked on the synthesis of vitamin C and the use of algin, pectin, and other carbohydrates as components of dry cells. After the War, when the mildly radioactive elements 14C and 3H became available, chemists realized that much chemical and biological information could be obtained from... 

---