期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1991
卷号：88
期号：5
页码：1746-1750
DOI：10.1073/pnas.88.5.1746
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：We have isolated, characterized, and partially sequenced immunoglobulin from the most primitive extant nonvertebrate craniate, the hagfish, a jawless fish that may have diverged from the vertebrate lineage more than 500 million years ago. The 160-kDa protein, which is a minor serum component, is composed of two different heavy chains of 69 and 74 kDa and a light chain of 29 kDa and resembles known immunoglobulin on the basis of an equimolar ratio of heavy and light chains, N-linked glycosylation of heavy chains, presence of intra- and interchain disulfide bonds, and polydispersity of each peptide chain. High molecular mass (polymeric) as well as low molecular mass (monomeric) forms were isolated from serum. The hagfish immunoglobulin is unique in that each heterodimer is composed of two different heavy chains and two light chains. The partial peptide maps and amino acid compositions of the two heavy chains differ; the chains do not crossreact immunologically. Slight crossreactivity of the 74-kDa heavy chain with antisera against purified shark immunoglobulin and some conservation of amino acid sequences, including those surrounding a cysteine, suggest that the isolated protein is an immunoglobulin.
