Monoclonal antibodies selectively reacting with the high molecular weight neurofilament proteins (NF 150K and NF 200K) on immunoblots of bovine spinal cord extracts were obtained upon immunization of mice with chicken brain antigen and with highly purified NF 150K or NF 200K isolated from bovine spinal cord by anion exchange chromatography. Antibodies reacting with NF 200K or with both NF 150K and NF 200K were selected for this study. The antibodies were screened on immunoblots for reactivity with phosphorylated epitopes by dilution of the supernatants in sodium potassium phosphate as well as by treatment of nitrocellulose transfers with alkaline phosphatase. Abolishment of staining under these conditions was taken as evidence of reactivity with phosphorylated epitopes. With phosphate/phosphatase‐sensitive antibodies, NF 200K immunoreactivity was a late event in rat optic nerve development. It was first observed at day 18 on immunoblots of sodium dodecyl sulfate extracts analyzed by gel electrophoresis. Conversely, with phosphate/phosphatase‐insensitive antibodies, NF 200K immunoreactivity was already present on day 10, the earliest age in this study. With one monoclonal reacting with phosphorylated NF 150K and NF 200K, NF 150K immunoreactivity was already present on day 10. It is proposed that NF 200K expression precedes NF 200K phosphorylation in development.

Three bovine intermediate filament proteins glial fibrillary acidic protein desmin the 70 kDa component of the neurofilament are compared by cleavage at cysteine tryptophan. The results of these experiments show that the difference in molecular weight between the glial fibrillary acidic protein desmin is due to a longer portion of the desmin amino terminal to the tryptophan. On the other hand the 70 kDa protein contains a carboxy terminal addition. The tryptophan cysteine contents of these proteins are also determined by amino-acid analysis. Differences in the apparent amount of cysteine determined by these methods in the glial fibrillary acidic protein 70 kDa proteins are discussed. Interchain disulfide bonds result in the formation of dimers in glial fibrillary acidic protein. The bovine 70 kDa neurofilament protein desmin also form dimers under nonreducing conditions. This emphasizes the structural similarity of these intermediate filament proteins

In the present study we report self‐assembly of individual neurofilament (NF) triplet proteins (70K, 150K, and 200K daltons) isolated by anion exchange chromatography from bovine spinal cord. Formation of smooth 10‐nm filaments by both NF 150K and NF 70K is shown. Optimal conditions for NK 150K filament formation were incubation in 100 mM MES, 0.2 M NaCl, 1 mM DTT, 0.5 mM EGTA, pH 6.5, at 37°C for 24 hr. Under the same assembly conditions, NF 200K formed 7‐nm coiled structures. These thin filaments were similar to those formed by NF 70K and 150K under less than optimal conditions. Our results indicate that NF 150K is an integral part of the filament (self‐assembly of NF 70K was previously demonstrated by others). We suggest that the optimal conditions resulting in the formation of a 10‐nm 200K homopolymer remain to be determined and that the thin coiled structures formed by all three NF proteins are protofilaments that coalesce to form a double helical 10‐nm filament.

The C-phycocyanin from the marine blue-green alga, Agmenellum quadruplicatum, has been isolated and purified to electrophoretic homogeneity. This is the first C-phycocyanin for which a low resolution three dimensional structure has been published (Hackert, M.L., Abad-Zapatero, C., Stevens, S.E. Jr. and Fox, J.L. (1977), J. Mol. Biol. 111, 365–369 and Abad-Zapatero, C., Fox, J.L. and Hackert, M.L. (1977) Biochem. Biophys. Res. Commun. 78, 266–272). The native C-phycocyanin complex shows an absorption maximum at 622 nm and another peak at 355 nm. In urea solutions, the 622 nm maximum of whole C-phycocyanin is shifted to 662 nm. Am662 = 94400 was determined. The fluorescence emission maxima at 650 nm for holoprotein is shifted and largely quenched in acid urea. The monomeric protein consists of two poly-peptide chains with molecular weights of 16 000 for the α chain and 18 500 for the β chain. Spectra in 8 M urea indicate that the α chain possesses one and the β chain two phycocyanobilin chromophores. The isolated chains show absorption maxima at 622 nm for the α chain and 608 nm for the β chain. Amino acid compositions of the holoprotein and the separated chains are given and N-terminal amino acid sequences are presented.