Proteins transported in slow components a and b of axonal transport are distributed differently in the transverse plane of the axon.

The distribution of the proteins migrating with the slow components a (SCa) and b (SCb) of axonal transport were studied in cross-sections of axons with electron microscope autoradiography. Radiolabeled amino acids were injected into the hypoglossal nucleus of rabbits and after 15 d, the animals were killed. Hypoglossal nerves were processed either for SDS-polyacrylamide gel electrophoresis fluorography to identify and locate the two components of slow transport, or for quantitative electron microscope autoradiography. Proteins transported in SCa were found to be uniformly distributed within the cross-section of the axon. Labeled SCb proteins were also found throughout the axonal cross-section, but the subaxolemmal region of the axon contained 2.5 times more SCb radioactivity than any comparable area in the remainder of the axon.

Axonal transport of calmodulin: a physiologic approach to identification of long-term associations between proteins.

Calmodulin is a soluble, heat-stable protein which has been shown to modulate both membrane-bound and soluble enzymes, but relatively little has been known about the in vivo associations of calmodulin. A 17,000-dalton heat-stable protein was found to move in axonal transport in the guinea pig visual system with the proteins of slow component b (SCb; 2 mm/d) along with actin and the bulk of the soluble proteins of the axon. Co-electrophoresis of purified calmodulin and radioactively labeled SCb proteins in two dimensional polyacrylamide gel electrophoresis (PAGE) demonstrated the identity of the heat-stable SCb protein and calmodulin on the basis of pI, molecular weight, and anomalous migration in the presence of Ca2+-chelating agents. No proteins co-migrating with calmodulin in two-dimensional PAGE could be detected among the proteins of slow component a (SCa; 0.3 mm/d, microtubules and neurofilaments) or fast component (FC; 250 mm/d, membrane-associated proteins). We conclude that calmodulin is transported solely as part of the SCb complex of proteins, the axoplasmic matrix. Calmodulin moves in axonal transport independent of the movements of microtubules (SCa) and membranes (FC), which suggests that the interactions of calmodulin with these structures may represent a transient interaction between groups of proteins moving in axonal transport at different rates. Axonal transport has been shown to be an effective tool for the demonstration of long-term in vivo protein associations.

Paraproteinemia in patients with acquired immunodeficiency syndrome (AIDS) or lymphadenopathy syndrome (LAS).

Eight of 15 patients with acquired immunodeficiency syndrome (AIDS) and six of nine patients with lymphadenopathy syndrome (LAS) had paraproteins in their sera. Twelve of these 14 were IgG kappa; the other two had no demonstrable light chains. The relationship of the paraprotein to the pathogenesis of AIDS is not clear, but we discuss its relation to derangements of B-cell immune regulation and function and to B-cell tumors in AIDS patients.

Resolution and reconstitution of Rhodospirillum rubrum pyridine dinucleotide transhydrogenase. II. Solubilization of the membrane-bound component.

The Rhodospirillum rubrum pyridine dinucleotide transhydrogenase system is comprised of a membrane-bound component and an easily dissociable soluble factor. Active transhydrogenase complex was solubilized by extraction of chromatophores with lysolecithin. The membrane component was also extracted from membranes depleted of soluble factor. The solubilized membrane component reconstituted transhydrogenase activity upon addition of soluble factor. Various other ionic and non-ionic detergents, including Triton X-100, Lubrol WX, deoxycholate, and digitonin, were ineffectual for solubilization and/or inhibited the enzyme at higher concentrations. The solubilized membrane component was significantly less thermal stable than the membrane-bound component. None of the pyridine dinucleotide substrate affected the thermostability of the solubilized membrane-bound component, whereas NADP+ and NADPH afforded protection to membrane-bound component. NADPH stimulated trypsin inactivation of membrane-bound component to a greater extent that NADP+, but inactivation of solubilized membrane component was stimulated to the same extent by both pyridine dinucleotides. The solubilized membrane component appears to have a slightly higher affinity for soluble factor than does the membrane-bound component.