Isolation and properties of gamma-tocopherol methyltransferase in Euglena gracilis.
Gamma-Tocopherol methyltransferase (EC2.1.1.-), which catalyzes the conversion of gamma-tocopherol into alpha-tocopherol, was present in a cell homogenate of Euglena gracilis. The enzyme was loosely bonded to the outer membrane of chloroplasts and solubilized from chloroplast membranes by a detergent, followed by partial purification in a three-step procedure. The methyltransferase showed a pH optimum of 7.5 and a temperature optimum of 35 degrees C and had an M(r) of 150,000. The activity was about 1.4-fold higher with gamma-tocopherol than with beta-tocopherol as substrate. The enzyme was specific for S-adenosylmethionine as a methyl donor, with a Km value of 50 microM. The addition of homogentisate, L-tyrosine and L-phenylalanine into a suspension of Euglena cells increased the relative pool sizes of alpha- and gamma-tocopherol, but not those of beta- and delta-tocopherol. The contents of alpha- and gamma-tocopherol in a chloroplast fraction of Euglena were always higher than those of any other fraction after any period of incubation with homogentisate. Based on the results of the present experiments, we propose a biosynthetic pathway of alpha-tocopherol in Euglena gracilis.
Shigeoka
S
S
Department of Food and Nutrition, Kinki University Nara, Japan.
Ishiko
H
H
Nakano
Y
Y
Mitsunaga
T
T
D000818:Animals; D002736:Chloroplasts / Q000201:enzymology; D003600:Cytosol / Q000201:enzymology; D005056:Euglena gracilis / Q000201:enzymology*; D008780:Methyltransferases / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism; D013347:Subcellular Fractions / Q000201:enzymology; D014810:Vitamin E / Q000096:biosynthesis*
D014810:Vitamin E; D008780:Methyltransferases; C047259:gamma-tocopherol methyltransferase