Protein radiochemical reactions

The major radiochemical reactions in aqueous protein systems are the result of free radical attack at the peptide bond, resulting in the formation of a carbonyl and amide or ammonia (14)-... 

The study of radiochemical yields in such analytically difficult and variable systems as meat proteins is a complex problem. Fortunately, however, both chemical (4,12,23,46,49) and electron spin reasonance studies (6,16, 22-25, 42) by several workers have shown that the major radiochemical reactions in proteins closely parallel those of simple peptides and amino acids, justifying the use of these simpler systems for preliminary radiochemical investigations. 

We have been unable to demonstrate any reaction between cyanatryn -oxide and DNA in vitro or between cyanatryn and liver DNA in vivo(2). Three hours after oral doses of []cyanatryn giving about 2 (1.98 and 2.41) yg of cyanatryn equivalents per g of liver, the perfused livers were removed, pooled and used to prepare protein, RNA and DNA fractions(14). Values expressed as yg of cyanatryn per g of pooled liver were total, 2.19 protein, 0.29 RNA fractions, 0.002 DNA fraction, not detectable. Radiochemical in the combusted sample of DNA was not detectable, i.e. less than 1 dpm/mg. This value is equivalent to 1 mol of triazine to 10 mol of guanine. Cyanatryn and its -oxide apparently possess low reactivity towards nitrogen nucleophiles. 

Figure 9. Radiochemical and protein analysis of column fractions after hydroxyapatite column chromatography of plasmin-treated (3-casein for various reaction times , total activity or specific activity, Fraction 1 M, total activity, Fraction 2 , specific activity, residual /3-casein O, total protein, Fraction 1. Values for total protein and total activity have been adjusted to correspond to trie same amount of total protein (21.92 mg) applied to each column (28).

This enzyme is a biotin protein. It also catalyses transcarboxylation reactions. The reaction shown here is an important step in fatty acid synthesis utilising malonyl CoA as an intermediate. It may be assayed radiochemically using C labelled KHCO3 in a reaction which is stopped by the addition of 6 N HCl [180]. 

This enzyme is a pyridoxal phosphate protein which can also catalyse reactions with hydroxyphenylalanine and 3-hydroxyphenylserine. It catalyses the formation of dopamine which is the precursor of noradrenaline. It may be assayed radiochemically utilising the evolution of C labelled CO2. 

This enzyme is a pyridoxal phosphate protein, which catalyses the formation of 7-aminobutyric acid, a possible chemical transmitter in the CNS. It can be used in an indicator reaction for the radiochemical assay of transaminases. It is assayed radiochemically using Clabelled glutamate and COj evolution [391]. 

This enzyme is a biotin-containing protein which catalyses a rate-limiting step in gluco-neogenesis from pyruvate. It can be assayed by u.v. spectroscopy using malate dehydrogenase in an indicator reaction [585] or radiochemically by incorporation of C labelled bicarbonate into oxalacetate stabilised by conversion to its 2,4-dinitrophenyl-hydrazone [586]. 

The ADA assay was done by a radiochemical method using an automated HPLC system (5). ADA activity was measured by the conversion of ( C) adenosine to ( C) inosine. The reaction was linear with time and protein concentration. Specific activity was expressed as nanomoles/min/mg of protein. 

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