The complete amino acid sequence of the mouse ,g chain from the BALB/c myeloma tumor MOPC 104E is reported. The CA region contains four consecutive homology regions of approximately 110 residues and a COOH-terminal region of 19 residues. A comparison of this p chain from mouse with a complete ;& sequence from human (Ou) and a partial A chain sequence from dog (Moo) reveals a striking gradient of increasing homology from the NH2-terminal to the COOH-terminal portion of these It chains, with the former being the least and the latter the most highly conserved. heavy chains held together by a third type of polypeptide designated the J chain (9). It is not known whether the membrane-bound and secreted ,u chains have the same polypeptide structure. Finally, after the IgM molecule binds antigen, the C,4 domain activates the effector pathways of the complement system (10).In this paper we report the amino acid sequence of the secreted ,. chain derived from the mouse myeloma tumor MOPC 104E. The mouse ti chain is compared with a human ,u chain whose sequence has been completely determined (11) and a dog ,q chain whose sequence has been partially determined (12, 13). As previously observed when the human ,u sequence and the dog At partial sequence were compared, there is a striking gradient of sequence homology, with the COOH-terminal homology regions significantly more conserved than the NH2-terminal homology regions (12). Several structural features of the ,u chain are highly conserved, including the placement of disulfide bridges and the locations of tryptophan residues and carbohydrate moieties in the constant region. t To whom reprint requests should be addressed.

ABSTRACT1-10 tM ATP stimulated H+ uptake and slowed the release of H+ in the dark in chloroplasts illuminated at pH values at which photophosphorylation can occur, but not at pH 6.5. This ATP stimulation of H + uptake was abolished by an antiserum to the chloroplast coupling factor and was reduced by the energy transfer inhibitors phlorizin and Dio-9. ATP synthesis after illumination was also enhanced by ATP. Electron flow from water to methyl viologen was inhibited by the same low concentrations of ATP.ADP also increased the extent of H+ uptake in chloroplasts, even in the presence of arsenate and MgCI2. In the presence of hexokinase and glucose, as well as arsenate and Mig ++, ADP inhibited H + uptake. The failure of previous investigators to observe a direct inhibition of H+ uptake by phosphorylation was probably caused by a masking of the inhibition by the stimulation of H + uptake by ATP. Furthermore, the stimulation of H+ uptake by ATP provides an explanation for its inhibition of electron flow.Although there is little doubt that the energy stored in gradients of H+ concentration across chloroplast membranes may be used to drive the synthesis of ATP (1), the relationship between light-dependent H+ uptake (2) and photophosphorylation is not clear. In general, H+ uptake in chloroplasts has properties remarkably similar to those predicted by the chemiosmotic theory of Mitchell (3). H+ uptake is sensitive to uncouplers of photophosphorylation (2) and generates rather large transmembrane gradients in H+ concentration (4,5).If the H+ gradient were the driving force for phosphorylation, or if ATP synthesis and H+ uptake are driven by a common intermediate, phosphorylation should decrease the extent of H+ uptake. The accumulation of either NH4+ (6) or of ethylamine (5) in spinach chloroplasts, which is a reflection of H+ uptake, is inhibited by phosphorylation. In contrast, H+ uptake in lettuce chloroplasts was found by Karlish and Avron (7) tional change may reduce the permeability of the membranes to H+. These observations help to explain the results of Karlish and Avron (7) and why ADP and ATP inhibit electron transport (9).

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The complete amino acid sequence of the mouse mu chain secreted by the MOPC 104E myeloma tumor has been determined. There are four constant region domains in the mu chain and a 20-residue COOH-terminal segment that plays a role in the polymerization of pentameric immunoglobulin M molecules. There are six sites of carbohydrate attachment in the MOPC 104E mu chain. Three complex-type and two high-mannose oligosaccharides are located in the mu chain constant region. The general type and location of carbohydrate moieties in the mu chain constant region are completely conserved between mouse and human mu chains. Homology in the location of carbohydrate structures on different classes of heavy chains is discussed.