Furukawa K, Matsuta K, Takeuchi F, Kosuge E, Miyamoto T, Kobata A
Department of Biochemistry, Institute of Medical Science, University of Tokyo, Japan.
Int Immunol. 1990;2(1):105-12. doi: 10.1093/intimm/2.1.105.
The sugar chains of IgG samples purified from sera of patients with rheumatoid arthritis (RA) contain many fewer galactose residues than those from sera of healthy individuals. Enzymatic studies revealed that the low galactose content in the IgGs of RA patients results from the reduced activity in the B cells of a galactosyltransferase (EC 2.4.1.90), which preferentially transfers galactose to asialo-agalacto-IgG. Asialo-agalacto-transferrin and asialo-ovine submaxillary mucin were also galactosylated by detergent-activated human B cell homogenates. However, no difference in the enzymatic activities toward these two acceptors was detected between the B cells from RA patients and from non-RA patients and healthy individuals. Enzyme kinetic studies revealed that an affinity of the galactosyltransferase in the B cells from RA patients was lowered for UDP-Gal but not for asialo-agalacto-IgG, while the affinities for UDP-Gal and asialo-agalacto-transferrin of the galactosyltransferase were not changed between the B cells from RA patients and from non-RA patients and healthy individuals in accordance with their enzyme activities. The results indicated that the reduced galactosyltransferase activity toward asialo-agalacto-IgG in the B cells from RA patients can be ascribed to the lowered affinity for UDP-Gal.
从类风湿性关节炎（RA）患者血清中纯化的IgG样本的糖链所含半乳糖残基比健康个体血清中的少得多。酶学研究表明，RA患者IgG中低半乳糖含量是由于B细胞中半乳糖基转移酶（EC 2.4.1.90）活性降低所致，该酶优先将半乳糖转移至去唾液酸-去半乳糖基-IgG。去唾液酸-去半乳糖基转铁蛋白和去唾液酸-羊颌下粘蛋白也可被去污剂激活的人B细胞匀浆进行半乳糖基化。然而，在RA患者与非RA患者及健康个体的B细胞之间，未检测到对这两种受体的酶活性存在差异。酶动力学研究表明，RA患者B细胞中的半乳糖基转移酶对UDP-Gal的亲和力降低，但对去唾液酸-去半乳糖基-IgG的亲和力未降低，而RA患者与非RA患者及健康个体的B细胞之间，半乳糖基转移酶对UDP-Gal和去唾液酸-去半乳糖基转铁蛋白的亲和力与其酶活性一致，并未改变。结果表明，RA患者B细胞中对半乳糖基转移酶对去唾液酸-去半乳糖基-IgG活性降低可归因于对UDP-Gal的亲和力降低。
