Role of Protein Methylation in Cellular Proliferation and Differentiation (V) : ("Partial Purification and Characterization of Two Different Carboxyl O-Methyltransferases Active on hCs (MW;23 kDa)and Other 23 kDa Protein, Respectively, in Human Placenta")

다국어 초록 (Multilingual Abstract)

Two different protein carboxyl O-methyltansferase have been identified in human placenta and their properties have been compared.
1. One of them was found to be a cysteine carboxyl O-methyltransferase acting on a 23 kDa protein paritally purified from human placental cytosol and proved to be membrane bound. This enzyme showed optimum pH at around 8 and heat-lability. Divalent cations tested (Ca^+2, Mg^+2, Zn^+2, Co^+2, and Cu^+2) were inhibitory, Cu^+2 being the most potent inhibitor. The enzyme activity was activated markedly by GTP and was inhibited by AFC, a competitive inhibitor of cysteine carboxyl O-methyltransferase.
2. The other one was found to be a carboxyl O-methyltransferase active on hCS(MW : 23 kDa) and to be a cytosol enzyme. This enzyme showed optimum pH at around 6 was relatively heat labile. Among various cations(Ca^+2, Mg^+2, Zn^+2, Co^+2, and Cu^+2) Ca^+2 and Mg^+2 activated whereas Cu^+2 inhibited the enzyme. In contrast to cysteine carboxyl O-methytransferase, the carboxyl O-methytransferase active on human chorionic somatomammotropin(hCS) was not influenced by GTP and AFC. Unexpectedly, hypomethylated hCS cloned and expressed on E coli was appeared to be inappropriate as a substrate. Human growth hormone which is one of growth hormone family together with hCS proved to be not methylated by the enzyme, suggesting that two hormones is differently regulated to have a distinct biological function.

목차 (Table of Contents)

• ABSTRACT
• Introduction
• Materials and Methods
• Results
• Discussion
• References