Characterization of distinct forms of methionine adenosyltransferase in nucleated, and mature human erythrocytes and erythroleukemic cells.
Two peaks of methionine adenosyltransferase (MAT) activity from human erythrocytes were partially purified on a DEAE-cellulose column. Using anti-MAT antibodies, a 60 kDa form of MAT, referred to as rho was identified in peak I. Although rho represented the major MAT protein in crude erythrocyte extracts, the enzyme was very labile and accounted for only 6% of the total MAT activity. Peak II enzyme was stable, and consisted of the previously described catalytic alpha (53 kDa) subunit and the beta subunit (38 kDa), both of which are found in activated human lymphocytes and leukemic cells of lymphoid origin. Mature normal and polycythemic erythrocytes contained predominantly rho as the major MAT protein, while nucleated erythrocytes and reticulocytes contained predominantly the lambda (68 kDa), the major form found in resting human lymphocytes. Human erythroleukemic cells (HEL 92.1.7) contained the alpha, alpha' and beta subunits of MAT, and in this regard was indistinguishable from MAT found in activated lymphocytes and leukemic cells of lymphoid origin (Jurkat). Since rho was generated during the incubation of extracts from resting lymphocytes, which contain predominantly lambda, in the absence of protease inhibitors; the rho form of MAT appears to be derived from the lambda form by proteolytic cleavage. The data indicate that distinct forms of MAT are present at different stages of erythrocyte maturation and reveal the presence of a new form of MAT with reduced activity compared to previously described forms.
Langkamp-Henken
B
B
Research Service, Veterans Administration Medical Center 151, Memphis, TN 38104.
Geller
A M
AM
LeGros
H L
HL
Price
J O
JO
De la Rosa
J
J
Kotb
M
M
D002469:Cell Separation; D004912:Erythrocytes / Q000201:enzymology*; D005312:Fetal Blood; D006801:Humans; D004915:Leukemia, Erythroblastic, Acute / Q000201:enzymology*; D008716:Methionine Adenosyltransferase / Q000737:chemistry* / Q000302:isolation & purification
D008716:Methionine Adenosyltransferase