Determination of human low molecular weight kininogen by immunoassay.

It was the aim of the present investigation to develop a convenient method for determination of human kininogens. Using mono- and polyclonal antibody preparations an ELISA-system for specific determination of LMWK could be developed. In addition, the specificity of the monoclonal antibody suggests that their epitope in HMWK and its heavy chain is different to that in LMWK.

Binding specificities of purified porcine brain alpha- and beta-tubulin subunits and of microtubule-associated proteins 1 and 2 examined by electron microscopy and solid-phase binding assays.

In this study, the molecular interaction of separated alpha- and beta-tubulin with purified microtubule-associated protein 1 (MAP 1) and MAP 2 was studied using electron microscopy and solid-phase binding assays with 125I-radiolabeled proteins. Electron microscopy of proteins recovered from sodium dodecyl sulfate polyacrylamide gels and subsequently incubated in various combinations under conditions promoting tubulin polymer formation revealed that both subunits have binding sites for MAP 1 as well as MAP 2. Overlays of nitrocellulose-transblotted MAPs with electrophoretically separated tubulin subunits eluted from gels confirmed these results. In overlays of nitrocellulose-immobilized tubulin subunits with gel-eluted MAP 2, self-association of MAP 2, but no binding to tubulin was detected. However, overlays with MAP 1 and MAP 2 purified under nondenaturing conditions revealed binding of both MAPs to beta-tubulin. In addition, these experiments demonstrated binding of both MAPs to MAP 2 and to the neurofilament proteins NF 70, NF 150 and NF 200. It is concluded that both alpha- and beta-tubulin possess binding sites for MAP 1 as well as MAP 2, but that the accessibility and/or binding affinity of these sites are strongly dependent on the tertiary structure of proteins. The demonstrated in vitro binding of MAP 1 and MAP 2 to all three neurofilament proteins as well as to MAP 2 confirms their presumed role as cytoskeletal linking proteins.

Expression of simian virus 40 gene A affects tubulin stability.

The stability of tubulins present in crude extracts of untransformed BALB/c-3T3 mouse fibroblasts, Chinese hamster lung cells, and various of their simian virus 40 transformants was assessed by measurement of their individual colchicine-binding decay rates. In all cases studied the decays followed the kinetics of first-order reactions, and rates were reduced at low temperatures and by vinblastine sulfate. Under all assay conditions, including different temperatures and protein concentrations, tubulins of normal cells decayed considerably faster than those of simian virus 40-transformed cells. Experiments performed with a number of Chinese hamster lung cell clones transformed with temperature-sensitive simian virus 40 gene A mutants showed a clear correlation between increased tubulin stability and the expression of gene A function. These results suggest that it is T-antigen, the viral gene A product, that affects tubulin.