UDP-glucose:(6-methoxy)podophyllotoxin 7-O-glucosyltransferase from suspension cultures of Linum nodiflorum.
Cell cultures of Linum species store 6-methoxypodophyllotoxin (MPTOX), podophyllotoxin (PTOX) and related lignans as O-glucosides. UDP-glucose:(M)PTOX 7-O-glucosyltransferase has been detected and characterised in protein preparations of suspension-cultured cells of Linum nodiflorum L. (Linaceae). The maximal lignan glucoside contents in the cells are preceded by a rapid increase of the specific glucosyltransferase activity on day six of the culture period. MPTOX glucoside is the major lignan with up to 1.18 mg g(-1) of the cell dry wt which is more than 30-fold of the PTOX glucoside content. Of the three aryltetralin lignans tested as substrates, PTOX and MPTOX display comparable apparent K(m) values of 4.7 and 5.4 microM, respectively. 5'-Demethoxy-6-methoxypodophyllotoxin is converted with the highest velocity of 25.2 pkat mg(-1) while also possessing a higher K(m) of 14.7 microM. Two-substrate test series indicate that all three compounds compete for the active site of a single protein. The structurally similar lignan beta-peltatin acts as competitive inhibitor as well. However, the 6-O-glucosidation is most likely catalysed by a separate enzyme. The (M)PTOX 7-O-glucosyltransferase works best at a pH around 9 and a temperature around 35 degrees C. A 15-30% increase of the reaction rate is effected by the addition of 0.9 mM Mn(2+).
Berim
Anna
A
Institut für Pharmazeutische Biologie, Philipps-Universität Marburg, Deutschhausstr. 17A, D-35037 Marburg, Germany.
Ebel
Rainer
R
Schneider
Bernd
B
Petersen
Maike
M
D019597:Flax / Q000201:enzymology*; D005960:Glucosides / Q000737:chemistry / Q000378:metabolism; D005964:Glucosyltransferases / Q000378:metabolism*; D015394:Molecular Structure; D011034:Podophyllotoxin / Q000737:chemistry / Q000378:metabolism*; D013379:Substrate Specificity; D014532:Uridine Diphosphate Glucose / Q000378:metabolism*
D005960:Glucosides; D005964:Glucosyltransferases; D011034:Podophyllotoxin; D014532:Uridine Diphosphate Glucose