Synthesis and secretion of γ-globulin by lymph node cells. VI. Characteristics of the structure of immunoglobulin A and its pattern of secretion by appendix cell suspensions

Abstract

1. 1. Rabbit appendix cell suspensions incubated with [ 3H]leucine or [ 3H]galactose secreted [ 3H]immunoglobulin A as the principal immunoglobulin. After purification, such [ 3H]immunoglobulin A was essentially completely coprecipitable with immunoglobulin A specific antisera. Comparison of the heavy and light chains derived from a mixture of [ 3H]leucine labeled immunoglobulin A and nonradioactive colostral immunoglobulin A (after extensive reduction and alkylation in the presence of guanidine) revealed that the heavy chains of these immunoglobulins were dissimilar in their migration on Sephadex G-200, while their light chains migrated identically. Dissociation of [ 3H]immunoglobulin A and colostral immunoglobulin A with 5 M guanidine, without prior reduction, permitted the detection of several peaks on Sephadex G-200 chromatography. Disc-gel electrophoresis of the peak known to contain “T” piece confirmed its presence in colostral immunoglobulin A and demonstrated its absence in appendiceal [ 3H]immunoglobulin A. Similar results were obtained when the entire light chain fraction was subjected to electrophoresis. 2. 2. Examination of the rate of appearance of appropriately labeled intra- and extracellular [ 3H]immunoglobulin A revealed that some of the carbohydrate residues are acquired about 15–20 min after synthesis of the polypeptide chains. Observations concerning the pattern of secretion of immunoglobulin A are discussed in relation to the structure of this protein.