SUBSTRATE-SPECIFICITY OF CTP - PHOSPHOETHANOLAMINE CYTIDYLYLTRANSFERASE PURIFIED FROM RAT-LIVER

被引:12
|
作者
VERMEULEN, PS [1 ]
GEELEN, MJH [1 ]
VANGOLDE, LMG [1 ]
机构
[1] UNIV UTRECHT,VET BIOCHEM LAB,POB 80-176,3508 TD UTRECHT,NETHERLANDS
来源
BIOCHIMICA ET BIOPHYSICA ACTA-LIPIDS AND LIPID METABOLISM | 1994年 / 1211卷 / 03期
关键词
PHOSPHOLIPID METABOLISM; PHOSPHATIDYLETHANOLAMINE SYNTHESIS; CTP; PHOSPHOETHANOLAMINE CYTIDYLYLTRANSFERASE; SUBSTRATE SPECIFICITY; N-METHYLATED PHOSPHOETHANOLAMINE SUBSTRATE; LIVER; (RAT);
D O I
10.1016/0005-2760(94)90159-7
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
CTP: phosphoethanolamine cytidylyltransferase was recently purified to homogeneity from rat liver (Vermeulen, P.S., Tijburg, L.B.M., Geelen, M.J.H. and van Golde, L.M.G. (1993) J. Biol. Chem. 268, 7458-7464). The present study focuses on the specificity of this enzyme for phosphorylated bases with a varying degree of N-methylation. The apparent K(m) for phosphoethanolamine was 0.072 mM. As the number of N-methylated substituents on phosphoethanolamine increased, the apparent K(m) increased: 0.11 mM for phosphomonomethylethanolamine and 6.8 mM for phosphodimethylethanolamine. Introduction of a third N-methyl group did not further increase the K(m) value. The effect of N-methyl groups on the reaction velocity was far more pronounced. A decreased V(max) for the reaction was found as the number of N-methyl substituents increased: 1.52 and 0.24 mumol/min per mg protein for phosphoethanolamine and phosphomonomethylethanolamine, and 44 and 0.69 nmol/min per mg protein for phosphodimethylethanolamine and phosphocholine, respectively. Phosphomonomethylethanolamine, phosphodimethylethanolamine and phosphocholine were weak competitive inhibitors of the cytidylyltransferase catalyzed reaction when phosphoethanolamine was used as a substrate, with K(i) values of 7.0, 6.8 and 52.9 mM, respectively. The results show that this cytidylyltransferase is highly specific for phosphoethanolamine. Comparison of these data with previously reported information on the substrate specificity of CTP: phosphocholine cytidylyltransferase endorses the view that the two cytidylyltransferases are functionally different.
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页码:343 / 349
页数:7
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