Naturally occurring radiolabelled

The biosyntheses of the naturally occurring purine nucleoside antibiotics, 9-/i-n-arabino-furanosyladenine (Ara-A), 2 -chlorodeoxycoformycin (36), 2 -amino-2 -deoxyadenosine (37) and nucleocidin (38) from adenine or adenosine have been examined by radiolabelling and the results are reviewed <89MI 711-05). 

To provide adequate accountability in metabolism studies of the distribution of parent compound and metabolites in each crop, 1JC-radio labelled PBO was used. The use of radiolabelled PBO allows the distinction of parent compound and metabolites from naturally occurring plant compounds,... 

Phase IV residues result from the incorporation of the radiolabel from the pesticide into naturally occurring compounds, e.g., proteins and sugars. These residues are of no toxicological concern. 

A number of cyclic polyols also are known to occur (Fig. 15.13). myo-Inositol (62), widespread in animals, is a growth factor in yeasts and a group B vitamin. This compound, one of nine possible stereoisomers, is widespread in plants (six other isomers also are naturally occurring). When plant cells are incubated with radiolabeled myo-inositol, a large portion of the label appears in the pentose and uronic acid residues of the cell wall (Karr, 1976 Loewus and Loewus, 1980). myo-Inositol serves as a precursor for o-glucuronic acid (3). Furthermore, when glucose and other monosaccharides are incorporated into cell walls, myo-inositol appears to be an intermediate (Karr, 1976 Loewus and Loewus, 1980). Analytical techniques for the study of cyclitols and sugar alcohols (polyols) have been reviewed (Beck and Hopf, 1990 Loewus, 1990). 

Even though the conversion of Z to (OX)Z had been clearly demonstrated, the natural occurrence of (OX)Z needed to be confirmed. Therefore, extracts were obtained from young embryos of P. vulgaris and purified by a combination of Sephadex, DEAE and reversed phase HPLC columns. GC-MS analyses of the purified extracts resulted in the detection of (OX)Z and its ribonucleoside as well as O-xylosyldihydrozeatin ((OX) (diH)Z). Thus the O-xylosyl derivatives of Z are naturally occurring compounds. Incubation of embryos of two other species, P. coccineus and P. acutifolius, with radiolabeled Z also led to the formation of (OX)Z and its dihydro-derivative [24]. These results indicate that O-xylosylation occurs in three of the four Phaseolus species examined thus far, P. lunatus being the exception. The interspecific differences are further elaborated on in some of the following sections. 

Jasmonic acid and related compounds are widely distributed in plants. They possess plant hormone-like properties nevertheless, their endogenous regulatory roles have to be confirmed further. Biotransformation in barley shoots of radiolabelled D J A and JA, respectively, gave the same pattern of metabolites which could be related to some naturally occurring JA analogues and conjugates. The major metabolic steps are ... 

Most insect herbivores appear to be rather effectively repelled by furanocoumarin-containing plants (21-24). A notable exception to this generalization occurs among some butterflies of the family Paplllonldae, whose caterpillars are adapted to feed successfully and in fact preferentially on plants that contain linear, but not angular, furanocoumarlns (22). These circumstances prompted us to undertake studies with the black swallowtail butterfly (Papilio polyxenes) and radiolabeled furanocoumarlns in attempts to elucidate the nature of the Insect/furanocoumarln Interactions Involved. 

The metabolic study, considered separately, consists of treatment of the animal with the radiolabeled compound followed by chemical analysis of all metabolites formed in vivo and excreted via the lungs, kidneys, or bile. Although reactive intermediates are unlikely to be isolated, the chemical structure of the end products may provide vital clues to the nature of the intermediates involved in their formation. The use of tissue homogenates, subcellular fractions, and purified enzymes may serve to clarify events occurring during metabolic sequences leading to the end products. 

Many derivatives of histidine are not stable to acid hydrolysis and are not discussed here (however, see 2.12.2 for those that occur naturally in proteins). Brief mention should be made of the iodination of histidyl residues by HOI ( 3.7.2). The mono- and diiodohistidines can be identified and distinguished from the iodinated tyrosines by high voltage paper electrophoresis in 1 M formic acid (Roholt and Pressman 1972) after complete enzymic hydrolysis of the protein or peptide ( 2.11 Roholt and Pressman 1972). Quantitation and identification are facilitated by the use of radiolabeled reagent. 

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