TY - JOUR
T1 - CATECHOL‐O‐METHYLTRANSFERASE IN RAT ERYTHROCYTE AND THREE OTHER TISSUES
T2 - COMPARISON OF BIOCHEMICAL PROPERTIES AFTER REMOVAL OF INHIBITORY CALCIUM
AU - Quiram, D. R.
AU - Weinshilboum, R. M.
PY - 1976/11
Y1 - 1976/11
N2 - The biochemical characteristics of soluble catechol‐O‐methyltransferase (COMT) activity in rat erythrocytes were compared with the properties of the soluble enzyme in rat liver, heart, and brain. COMT was measured by a procedure that avoided artifacts of some other assay procedures including inhibition of the enzyme by endogenous calcium. After the removal of calcium from the reaction mixture the apparent Michaelis‐Menten constants for the two cosubstrates of the COMT reaction, S‐adenosyl‐1‐methionine (SAM) and 3,4‐dihydroxybenzoic acid (DBA), were similar in tissue preparations of rat liver, brain, heart and blood. The apparent Km, values for the four tissues ranged from 5.7 to 6.7 × 10−6M and from 0.9−1.4 × 10−4M for SAM and DBA, respectively. The optimal pH and the optimal concentration of magnesium for the assay of red blood cell COMT were also similar to those for the enzyme in the three other rat tissues. After the removal of endogenous calcium, COMT activity in all four tissues was inhibited by the addition of calcium, and the [CaCl2] necessary to inhibit the enzyme activity 50% was 3−5 × 10−4M in all cases. The relative activities of COMT in the rat heart, brain, erythrocyte, and liver when expressed per g tissue or per ml of packed red blood cells were 1 to 1.15 to 1.58 to 140, respectively.
AB - The biochemical characteristics of soluble catechol‐O‐methyltransferase (COMT) activity in rat erythrocytes were compared with the properties of the soluble enzyme in rat liver, heart, and brain. COMT was measured by a procedure that avoided artifacts of some other assay procedures including inhibition of the enzyme by endogenous calcium. After the removal of calcium from the reaction mixture the apparent Michaelis‐Menten constants for the two cosubstrates of the COMT reaction, S‐adenosyl‐1‐methionine (SAM) and 3,4‐dihydroxybenzoic acid (DBA), were similar in tissue preparations of rat liver, brain, heart and blood. The apparent Km, values for the four tissues ranged from 5.7 to 6.7 × 10−6M and from 0.9−1.4 × 10−4M for SAM and DBA, respectively. The optimal pH and the optimal concentration of magnesium for the assay of red blood cell COMT were also similar to those for the enzyme in the three other rat tissues. After the removal of endogenous calcium, COMT activity in all four tissues was inhibited by the addition of calcium, and the [CaCl2] necessary to inhibit the enzyme activity 50% was 3−5 × 10−4M in all cases. The relative activities of COMT in the rat heart, brain, erythrocyte, and liver when expressed per g tissue or per ml of packed red blood cells were 1 to 1.15 to 1.58 to 140, respectively.
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U2 - 10.1111/j.1471-4159.1976.tb00327.x
DO - 10.1111/j.1471-4159.1976.tb00327.x
M3 - Article
C2 - 12170607
AN - SCOPUS:0017084582
SN - 0022-3042
VL - 27
SP - 1197
EP - 1203
JO - Journal of neurochemistry
JF - Journal of neurochemistry
IS - 5
ER -