The metabolism and residues of 2,2-dichlorovinyl dimethyl phosphate-P32 (DDVP or Vapona) were examined with rats, cows, and a goat. Studies with rats also utilized carbon14 labeled DDVP, dichloroacetaldehyde, and dichloroethanol, and phosphorus32-labeled O-methyl 2,2-dichlorovinyl phosphate and , -dimethyl phosphate. In addition, several rats and a single cow were treated orally with 1,2-dibromo-2,2-dichloroethyl dimethyl phosphate-P32 (Dibrom). These insecticides are rapidly hydrolyzed in mammals to yield no persisting tissue residues and only trace levels in milk. The initial phosphoruscontaining metabolites of DDVP, , -dimethyl phosphate and O-methyl 2,2-dichlorovinyl phosphate, are low in toxicity and rapidly excreted or further degraded. The 1 -carbon of the 2,2-dichlorovinyl group in DDVP is excreted in urine predominantly as a conjugate of dichloroethanol, probably the glucuronide, in the feces as unknown derivatives, and in the expired air as carbon dioxide. Small amounts of dichloroacetic acid may be formed, and some of the C14 persists in liver, blood, and other tissues in an unidentified form. Limited metabolism studies of DDVP in plants and of DDVP and Dibrom in bovine rumen fluid are also reported.
The influence of iodoacetamide and N-ethylmaleinimide on the activity of the acetyl transferase component of fatty acid synthetase from baker's yeast was studied using [Wlacetyl-CoA and pantetheine as substrates. No inhibition by either of the blocking agents was observed. This, together with previous information, suggests, that a non-sulfhydryl acceptor group is involved in the catalytic process of acetyl transfer from acetyl-CoA to the acyl carrier protein component of the multienzyme complex.To identify this carrier group in the active site of its acetyl transferase, fatty acid synthetase was treated with [14C]acetyl-CoA after first blocking the free SH-groups of the complex with Ellman's reagent. I n this way a radioactive acetyl-enzyme was formed, which By comparing the amino acid composition of [14C]malonyl-peptides, stable towards performic acid, with the partial sequence of the [14C]acetyl-enzyme it was concluded that acetyl and malonyl transfer reactions are catalyzed by enzyme components of the multienzyme complex, which are distinctly different. I n both cases however, the catalytic mechanisms probably involve the participation of serine residues as acyl carrier groups. 19 Eur.
It was shown by gel electrophoresis in sodium dodecylsulphate solution that 3-methylcrotonylCoA carboxylase from Achromobacter IVS is composed of two different subunits with molecular weights of about 78000 and 96000, respectively. The biotin is bound to the heavier subunit. It was previously found that 3-methylcrotonyl-CoA carboxylase contains four biotin molecules per complex. A complex composed of four of each subunit would thus have a molecular weight of about 700 000. This is compatible with the molecular weight of 760000 determined earlier by analytical ultracentrifugation.Both subunits were isolated preparatively. As the subunits, unlike the complex, are very sensitive to oxygen, special precautions had to be taken during isolation. The biotin-containing subunit was isolated by chromatography on DEAE-cellulose in 5 M urea. It no longer catalyzed the overall reaction, yet could still carboxylate free biotin. The biotin-free subunit was separated after dissociation of the enzyme by three-days' dialysis at pH 9.8 under nitrogen. On chromatography over a Sepharose-bound avidin column, the biotin-subunit was fixed and the biotin-free subunit was eluted unretarded. The latter subunit showed no enzymic activity. After the addition of the biotin-containing subunit, overall activity was regenerated.The speed of reassociation is very much enhanced by 3-methylcrotonyl-CoA. It was shown by reassociation experiments under different conditions that probably an initial complex A,B, is formed, possessing a binding site for 3-methylcrotonyl-CoA. Upon the binding of this substrate the conformation may be changed to a form favourable for reconstitution.Finally, the structures of biotin enzymes from different sources are compared. In the course of evolution there is a tendency toward integration of the different constituent proteins into only one polypeptide chain.3-Methylcrotonyl-CoA carboxylase, a biotincontaining enzyme, catalyzes the following reaction : 0
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