Hydrogen exchange in the synthesis of glyceryl ether and in the formation of dihydroxyacetone in Tetrahymena pyriformis

Abstract

We have previously shown that [l,3-3H]dihydroxyacetone phosphate is incorporated enzymatically into O-alkyl lipids with the loss of one tritium from C-3. Further evidence for a tritium exchange has been presented in this investigation by showing, in a microsomal system from Tetrahymena pyriformis, that tritiated O-alkyl lipids are formed in the presence of tritiated water from dihydroxyacetone phosphate and hexadecanol. In another series of experiments we have shown that tritiated dihydroxyacetone phosphate yields tritiated acyldihydroxyacetone (via acyldihydroxyacetone phosphate) T A he known steps m O-alkyl-DHAP1 synthesis include the initial formation of acyl-DHAP from fatty acid and DHAP in the presence of ATP, magnesium, and coenzyme A. Acyl-DHAP, hexadecanol, ATP, and magnesium then interact to form O-alkyl-DHAP (Hajra, 1970;Wykle et al., 1972). In this process it is known that the oxygen of hexadecanol is retained in the product (Snyder et al., 1970).When [1,3-3H]dihydroxyacetone phosphate is incorporated enzymatically into O-alkyl lipids, there is a loss of half of the tritium atoms from C-32 (Friedberg et al., 1971). Since there is no net loss of hydrogen in the product, the findings point to an exchange reaction. It is also known that this reaction is specific for the same hydrogen lost in the triosephosphate isomerase reaction, but not the one lost in the fructose-1,6diphosphate aldolase reaction (Friedberg et al., 1972).The present investigation was undertaken to obtain more information on the nature of the hydrogen loss which occurs in the formation of O-alkyl lipids. Evidence will be presented to show that the tritium lost from [1,3-3H]dihydroxyacetone phosphate is exchanged with a hydrogen from the aqueous environment and that this exchange occurs on C-3 of the dihydroxyacetone phosphate moiety. It will also be shown that the hydrogen loss depends on the presence of coenzyme A, that acyldihydroxyacetones are formed without loss of hydrogen, and that the number of hydrogen atoms exchanged greatly exceeds the number of moles of O-alkyl lipid formed. The difference is in part or entirely accounted for by the formation of dihydroxyacetone. The formation of this compound also involves a hydrogen exchange. This finding will be discussed.

Biosynthesis of the C18 family of cutin acids. ι-Hydroxyoleic acid, ι-hydroxy-9,10-epoxystearic acid, 9,10,18-trihydroxystearic acid, and their Δ12-unsaturated analogs

“…Thus, there appears to be a specific incorporation of the methylene-interrupted dienoic and trienoic acids into the ether-linked core of cutin, suggesting that the ds-1,4pentadiene structure may be involved in the formation of ether bonds in cutin. One possible route of synthesis could involve displacement of an acyl function from in-chain esterified -ketol, produced by the action of lipoxygenase and hydroperoxide isomerase on linoleic acid (Veldink et al, 1970(Veldink et al, , 1972Zimmerman, 1966) in a manner similar to that observed in glyceryl ether biosynthesis (Hajra, 1970;Snyder et al, 1970;Friedberg and Heifetz, 1973), although a more nonspecific radical mechanism cannot be ruled out.…”

Formation of tritiated O-alkyl lipid from acyldihydroxyacetone phosphate in the presence of tritiated water

“…We have previously shown that when dihydroxyacetone phosphate (DHAP1) is used in the enzymatic formation of O-alkyl lipids, there is a hydrogen exchange from the carbon that acquires the O-alkyl moiety (Friedberg et al, 1971;Friedberg and Heifetz, 1973). This exchange is specific for the same hydrogen labilized in the triosephosphate isomerase reaction (Friedberg et al, 1972).…”

“…tiated water. In the microsomal system from Tetrahymena pyriformis, a concomitant reaction is the coenzyme A dependent formation of dihydroxyacetone from dihydroxyacetone phosphate (Friedberg and Heifetz, 1973). The dihydroxyacetone formed also appears to have undergone a hydrogen exchange, and the coenzyme A requirement was interpreted to indicate that acyldihydroxyacetone phosphate (acyl-DHAP) is a precursor of dihydroxyacetone.…”

Studies on the formation of dipalmitoyl species of phosphatidylcholine and phosphatidylethanolamine in pulmonary type II cells

“…Pulmonary type II cells, however, are rich in peroxisomes (Schneeberger, 1972;Hirai et al,1983) and therefore a high rate of ether lipid formation can be expected. Although a direct comparison of diacyl-and ether-lipid synthesis with [1(3)-3H]glycerol as precursor is not possible, since one sn-I H atom is lost during the ether-bond formation (Friedberg & Heifetz, 1973), a high synthesis rate of ether lipids in pulmonary type II cells can be derived from the data of Table 1. Therefore the relative contributions of Gro-3-P and DHAP acylation for the synthesis of dipalmitoyl-PtdCho cannot be calculated correctly from the incorporation of these precursors into the total phospholipid fraction.…”