Biosynthesis of immunoglobulin A (IgA). Secretion and addition of carbohydrate to monomer and polymer forms of a mouse myeloma protein

Cell suspensions of mouse plasma-cell tumour MOPC 315 secreting predominantly IgA (immunoglobulin A) monomer and dimer were incubated with radioactive leucine, mannose, galactose and fucose for various periods of time. The amounts of secreted and intracellular immunoglobulins were measured by co-precipitation with specific antibody, and the molecular species present were assessed by electrophoresis in polyacrylamide gels. Analysis of the secreted myeloma protein demonstrated that monomer and dimer IgA molecules are identical with respect to carbohydrate composition and rate of secretion. Within the cell, the myeloma protein is almost entirely accounted for by monomer units which either leave the cell as such or are polymerized with the addition of J chain close to the time of secretion. The results support the concept of a stepwise addition of carbohydrate residues to IgA immunoglobulin during the process of secretion. Similar patterns of carbohydrate assembly were found for the monomer or dimer molecules. Mannose residues are added at an early stage, whereas fucose is added close to the time of secretion. Galactose is also added early, but some may also be incorporated at a later stage. Control of IgA polymerization is considered unlikely to reflect regulation at the level of carbohydrate addition, and it is suggested that the critical controlling factor is the J chain.     

EFFECTS OF LEUCINE ON BRAIN SEROTONIN

Abstract— The effect of excess leucine in the diet on serotonin metabolism in the brain was investigated in experimental animals. It was found that:
(1) Animals receiving diets containing 3 % and 8 % leucine and those receiving jowar diets had significantly lower levels of serotonin in the brain.
(2) Intraperitoneal administration of the precursor amino acid 5-HTP increased the serotonin concentration in brain in both control and leucine-fed animals. However, the serotonin concentration in leucine-fed animals was significantly lower than that of pairfed controls. Larger amounts of the synthesized serotonin were found to be catabolized in 3 hr in leucine-fed animals than in control animals.
(3) The in vitro uptake of [¹⁴C]5-HTP by brain slices of animals fed leucine was found to be similar to that of control animals.
(4) The basal concentration of 5-HIAA in brain was higher in leucine-fed animals, suggesting a higher rate of catabolism of serotonin.
(5) Administration of nicotinic acid resulted in a further fall of serotonin concentration in the brains of leucine-fed animals but not in control animals.     

Helical Nature of the Ciliary Beat of Paramecium multimicronucleatum*

SYNOPSIS. Phase and interference cinemicrographs of cilia of Paramecium multimicronucleatum, immersed 3–24 hours in 1.0% methyl cellulose, revealed that 1) in swimming Paramecium the cilia beat with a traveling helical wave from base to tip rather than with the back and forth movement usually assumed, 2) during ciliary reversal the cilia merely change direction, but continue to beat with a traveling helical wave, and 3) in stationary Paramecium the beat is conicoidal. The traveling wave appears as an undulatory wave about 1 1/4 wave lengths long in both surface and profile views, and therefore must be helical. Envelope of the wave is cylindrical except near the base. Observations were confirmed in media without methyl cellulose by means of high speed cinemicrography, up to 4000 frames/sec. The back and forth movement, as described in all textbooks and monographs, is based mostly on 1) analogy to the abfrontal cilia (cirri) of Mytilus, which do beat with a back and forth movement, and 2) conclusions drawn from fixed preparations which do not represent what actually happens in a living animal. In a stationary Paramecium the envelope of the beat is conicoidal as seen in profile, but probably is a spiral wave, i.e., similar to a helix but increasing in diameter from base to tip. This change in wave form could be caused by the increase in resistance of the water in a stationary organism over one that is moving. Cilia and flagella (also ciliates and flagellates) are usually distinguished on the basis of wave form, but the present observations, together with previous data on flagella, show that such distinctions are untenable.     

Synchrony of Long Duration in Suspension Cultures of Mammalian Cells

THE high-sulphur proteins of α-keratins, which constitute the non-filamentous matrix between the microfibrils, comprise several major groups of proteins, each group consisting of a number of closely related components. They are obtained in a soluble form by reduction of the disulphide bonds of wool and preferential extraction with alkaline thioglycollate at high ionic strength¹. The thiol groups are subsequently stabilized by alkylation with iodoacetic acid.