Interchain disulphide bridges of mouse immunoglobulin M.

Mouse IgM (immunoglobulin M) was selectively and partially reduced and treated with iodo[2-14C]acetate to label the interchain disulphide bridges. The carboxymethylation was studied in some detail. The labelled peptides were purified, sequenced and positioned by homology with human IgM. Only peptides originating from three interchain disulphide bridges were labelled, in contrast with the four labelled bridges obtained in human IgM under the same conditions. These peptides are homologous to human bridge peptides forming the heavy-light bridge and two inter-heavy bridges, one present in the CMU2 region and the other in the C-terminal region. The inter-heavy bridge in the Cmu2 region was alone cleaved and radioactively labelled in selectively reduced IgM held together as a pentamer by non-covalen interactions. The same bridge was the only one to be totally cleaved in subunits released after more extensive, though still selective, reduction. In the light of these results a possible arrangement of the disulphide bridges of the mouse IgM.     

STUDIES ON THE PHOTOBIOLOGY OF BANGIA FUSCOPURPUREA1

In the Rhodophyta there are few reports of light-mediated responses. In Bangia fuscopurpurea the formation of the fertile cell rows by the Conchocelis phase meets criteria established for the definition of photoperiodism in higher plants. Throughout the life history of the alga maintained in culture, cell fate and cell function fire under photoperiodic regulation. Maintenance and conversion photoperiods are established. Sequential induction studies suggest the absence of metabolic effects operative in the induction, response of fertile cell row formation. Preliminary studies of non-24-hr photoperiods suggest the absence of short-term endogenous rhythms involved in spore formation. A phytochrome response involved in the formation of the fertile cell rows is demonstrated.     

Some molecular properties of plant starch phosphorylases and the levels of activity of the multiple forms

A number of plant tissues have two phosphorylase fractions (I and II) that can be separated by DEAE-cellulose chromatography. When only one is detectable, it corresponds to enzyme II. Peas differed from other legumes in showing an increase in enzyme I during seed germination. Examination of the I type enzymes, by sodium dodecyl sulphate polyacrylamide gel electrophoresis, sector cell ultracentrifugation and gel filtration, indicated that these were dimers composed of similar sub-units of MW near 90 000. When phosphorylase II enzymes were examined, the sub-unit MW was found to be higher, near 110 000 and, whereas ultracentrifugation techniques indicated a dimer of similar sub-units for the native enzyme, gel filtration gave higher MW values. Phosphorylase II from Victory Freezer peas differed from the other samples, in being able to form mixtures of dimer and tetramer.