Saxena A, Fleming P J
J Biol Chem. 1983 Apr 10;258(7):4147-52.
Dopamine beta-hydroxylase is present in the bovine adrenal medulla in two forms, soluble and membrane bound. Previous isolation procedures for the membranous hydroxylase have resulted in a form of enzyme identical in subunit structure with the soluble type. We report here the isolation of a membrane-bound form of dopamine beta-hydroxylase which is structurally different from the soluble form. The isolated membranous enzyme has a large apparent molecular weight on gel filtration, is amphiphilic, and contains bound phospholipid which is predominantly phosphatidylserine. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate shows that the membranous hydroxylase contains two nonidentical subunits under both reducing and nonreducing conditions. Under reducing conditions the apparent molecular weights of the two subunits are 70,000 and 75,000 and both contain carbohydrate. The purified membranous hydroxylase binds to phospholipid vesicles and chymotryptic digestion of the bound enzyme suggests that two forms of the membranous hydroxylase exist.
多巴胺β-羟化酶在牛肾上腺髓质中以两种形式存在，即可溶性和膜结合型。先前用于分离膜结合型羟化酶的方法所得到的酶形式，其亚基结构与可溶性类型相同。我们在此报告分离出一种结构上不同于可溶性形式的膜结合型多巴胺β-羟化酶。分离出的膜结合型酶在凝胶过滤中具有较大的表观分子量，具有两亲性，并且含有主要为磷脂酰丝氨酸的结合磷脂。在十二烷基硫酸钠存在下进行的聚丙烯酰胺凝胶电泳表明，在还原和非还原条件下，膜结合型羟化酶均含有两个不同的亚基。在还原条件下，两个亚基的表观分子量分别为70,000和75,000，且都含有碳水化合物。纯化的膜结合型羟化酶与磷脂囊泡结合，对结合的酶进行胰凝乳蛋白酶消化表明存在两种形式的膜结合型羟化酶。
