Substrate specificity of cis-prenyltransferase in rat liver microsomes.
Long chain cis-prenyltransferase in rat liver microsomes was studied using various allylic isoprenoid substrates. Microsomes could utilize trans-geranyl pyrophosphate, but not cis-geranyl pyrophosphate for polyprenyl pyrophosphate synthesis. Both trans, trans-farnesyl pyrophosphate and trans,cis-farnesyl pyrophosphate were used as substrates with Km values of 24 and 5 microM, respectively. trans,trans,cis-Geranylgeranyl pyrophosphate could be used as substrate with an apparent Km of 36 microM. trans,trans,trans-Geranylgeranyl pyrophosphate was also utilized as substrate, but with a very low affinity. After pulse labeling for 4 min, using [3H]isopentenyl pyrophosphate and trans,trans-farnesyl pyrophosphate, the only product formed was trans,trans,cis-geranylgeranyl pyrophosphate, which, upon chasing, yielded polyprenyl pyrophosphate. Independent of the nature of the substrate used, even in the case of polyprenyl 12-pyrophosphate and all-trans-nonaprenyl pyrophosphate, the chain lengths of the products were identical, i.e. polyprenyl pyrophosphates with 15-18 isoprene residues. Microsomes were able to synthesize trans,trans-farnesyl pyrophosphate using trans-geranyl pyrophosphate as substrate. The results indicate that rat liver microsomes contain a farnesyl pyrophosphate synthase activity and that the reaction catalyzed by cis-prenyltransferase may consist of two individual steps, i.e. synthesis of trans,trans,cis-geranylgeranyl pyrophosphate and elongation of this product to long chain polyprenyl pyrophosphates.
Ericsson
J
J
Department of Biochemistry, Stockholm University, Sweden.
Thelin
A
A
Chojnacki
T
T
Dallner
G
G
D000818:Animals; D002851:Chromatography, High Pressure Liquid; D004122:Dimethylallyltranstransferase / Q000378:metabolism*; D007536:Isomerism; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D011106:Polyisoprenyl Phosphates / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013379:Substrate Specificity
D011106:Polyisoprenyl Phosphates; C015234:geranyl pyrophosphate; D004122:Dimethylallyltranstransferase