Isolation and primary structure of rat secretin

A major form of rat secretin was purified to homogeneity from small intestine, being detected with a porcine secretin radioimmunoassay throughout 7 chromatographic steps. The sequence of the heptacosapeptide amide H-S-D-G-T-F-T-S-E-L-S-R-L-Q-D-S-A-R-L-Q-R-L-L-Q-G-L-V-NH2 shows that rat secretin has a glutamine residue in position 14 instead of arginine as in pig secretin.     

Quantitative receptor autoradiography in the human brain

Summary Quantitative receptor autoradiography on sections of the human brain raises methodical problems of which some are relevant also for studies in animal tissue, but others are unique in studies of human brain tissue. Procedures for the following methodical aspects are discussed image analysis for quantitation of the regional distribution of receptor densities, saturation analysis on autoradiographs, influence of age and post-mortem delay and quenching of -radiation in brain tissue. The solutions proposed to these problems make receptor autoradiography in the human brain to a reliable method for studies of chemical neuroanatomy.     

Isotype switching of an immunoglobulin heavy chain transgene occurs by DNA recombination between different chromosomes

Transgenic mice carrying an immunoglobulin mu heavy chain transgene exhibit isotype switching of the transgene. We have now characterized the mechanism of transgene switching in these mice. The site of mu transgene insertion in one transgenic line has been localized to chromosome 5 using a series of polymorphic endogenous retroviruses as genetic markers in backcross mice. The endogenous immunoglobulin heavy chain locus resides on mouse chromosome 12, which shows that transgene isotype switching can occur between two different chromosomes even though normal antibody gene switching has generally been thought to occur within one chromosome. We find that transgene isotype switching involves interchromosomal DNA recombination, and our data suggest that the same enzymatic mechanisms mediate both normal isotype switch recombination and interchromosomal transgene switching. Our findings also support the notion that the isotype switching mechanism can induce chromosomal translocations such as observed for the c-myc gene in some B cell tumors.     

Photoactivation of rhodopsin involves alterations in cysteine side chains: detection of an S-H band in the Meta I-->Meta II FTIR difference spectrum.

FTIR difference spectroscopy has been used to study the role of cysteine residues in the photoactivation of rhodopsin. A positive band near 2550 cm-1 with a low frequency shoulder is detected during rhodopsin photobleaching, which is assigned on the basis of its frequency and isotope shift to the S-H stretching mode of one or more cysteine residues. Time-resolved studies at low temperature show that the intensity of this band correlates with the formation and decay kinetics of the Meta II intermediate. Modification of rhodopsin with the reagent NEM, which selectively reacts with the SH groups of Cys-140 and Cys-316 on the cytoplasmic surface of rhodopsin, has no effect on the appearance of this band. Four other cysteine residues are also unlikely to contribute to this band because they are either thio-palmitylated (Cys-322 and Cys-323) or form a disulfide bond (Cys-110 and Cys-187). On this basis, it is likely that at least one of the four remaining cysteine residues in rhodopsin is structurally active during rhodopsin photoactivation. The possibility is also considered that this band arises from a transient cleavage of the disulfide bond between cysteine residues 110 and 187.