Evidence for a reactive sulfhydryl in the DNA binding domain of the 1,25-dihydroxyvitamin D3 receptor

Evidence is presented here that organomercurial binding to a reactive sulfhydryl group is capable of altering the DNA-binding characteristics of the 1,25-dihydroxyvitamin D receptor (D-receptor). Accordingly, hormone-free receptor (R_o) binding to DNA-cellulose is inhibited in a concentration-dependent fashion with both HgCl₂ and p-chloromercuribenzene sulfonate (pCMBS) with complete inhibition evident at 1.0 mM. Further, low concentrations (0.5 mM) of mercurials are also capable of dissociating preformed DNA-receptor complexes, a process reversible with excess thiol reagent such as monothioglycerol. These findings are in contrast to alkylating reagents such as iodoacetamide, which is capable of only partially inhibiting the formation of the receptor-DNA duplex (37% at 25 mM). Once created, however, the duplex is completely insensitive to dissociation (even at 25 mM). These results imply that in addition to the association of a cysteine(s) moiety in or near the sterol binding site, modification of a similarly reactive group(s) can also alter the D-receptor's DNA-binding domain.     

Molecular heterogeneity in McArdle's disease

Biopsies were taken from a group of eleven patients with McArdle's disease, a congenital deficiency in muscle glycogen phosphorylase. The biopsies were screened by Western and Northern blotting for phosphorylase protein, phosphotrylase-bound pyridoxal-5′-phosphate (the cofactor of the enzyme) and for phosphorylase mRNA. Of the eleven patients, three expressed phosphorylase mRNA at near normal levels and at the expected size. One of these patients also expressed low levels of phosphorylase protein that correlated with a small amount of measurable phosphorylase activity. These data support the contention of molecular heterogeneity in the presentation of this phenotype.     

Characterization of the carcinoma-associated Tk antigen in helminth parasites

Expression of Tk antigen, a truncated carbohydrate antigen, was examined in helmith parasites. Using the monoclonal antibody LM389, this antigen was detected in extracts from Taenia hydatigena, Mesocestoides vogae (syn corti), and Taenia crassiceps. No reactivity was observed in Thysanosoma spp., Dipylidium caninum, Fasciola hepatica, and Nyppostrongylus brasiliensis. On the basis of their electrophoretic mobility, different patterns of Tk-bearing glycoproteins were observed among T. hydatigena, M. corti and T. crassiceps by immunoblotting, with certain components resolved as broad bands typical of mucin-like glycoproteins. Most Tk-reactive material remained in the 0.6 N perchloric acid-soluble fraction, confirming that Tk epitopes are carried by mucin-type glycoproteins. Immunohistochemical analysis revealed that in T. hydatigena, Tk antigen is mainly expressed in the tegument, whereas in M. corti the reactivity was principally observed in the subtegumental parenchyma. The presence of a novel tumor-associated carbohydrate antigen in invertebrates, contributes to strengthen the notion that truncated mucin-type O-glycosylation is a normal phenomenon in parasitic worms and may help identify new biological characteristics of helminth parasites.