Multiple Molecular Forms of Dopamine β-Hydroxylase in the C1300 Mouse Neuroblastoma Tumor and in the Serum of Tumor-Bearing Mice

Abstract: The distribution of the enzymatic activity of dopamine β-hydroxylase (DBH) in linear sucrose gradients was studied for a soluble fraction of the C₁₃₀₀ mouse neuroblastoma tumor, for the serum of tumor-bearing A/J mice, and for adrenal tissue and serum of control mice. In controls (adrenal gland and serum of A/J mice), about 75% of the DBH activity was associated with a high-molecular-weight form, denoted as DBHA_A, with an apparent sedimentation coefficient of 11.3 S. About 25% of the DBH activity was attributable to a slower-sedimenting species (7.1 S), denoted as DBHB_B. In tumor supernatants and in the serum of tumor-bearing mice, about 55% of the DBH activity was present as the 7.1 S species (DBHR_B), while only 35% was recovered as the high-molecular-weight form (DBHA_A). Approximately 5% of the activity could be attributed to a separate form, with a sedimentation coefficient of about 4.5 S. This form is designated DBH_C. The ratio DBHR/DBHA is significantly higher in tumor tissue and in serum of tumor-bearing mice than in controls. The three enzymically active forms of DBH in the C₁₃₀₀ tumor are considered to represent the tetrameric (DBHA_C), dimeric (DBH_B), and monomeric (DBH_C) forms of the enzyme.