Phosphorylation of the GABAA receptor by cAMP-dependent protein kinase and by protein kinase C: Analysis of the substrate domain

Previous work has shown that the GABA_A-receptor (GABA_A-R) could be phosphorylated by cAMP-dependent protein kinase (PKA), protein kinase C (PKC), and a receptor associated kinase. However, no clear picture has yet emerged concerning the particular subunit subtypes of the GABA_A-R that were phosphorylated by PKA and PKC. In the present report we show that an antibody raised against a 23 amino acid polypeptide corresponding to a sequence in the putative intracellular loop of the 1 subunit of the receptor blocks the in vitro phosphorylation of the purified receptor by PKA and PKC. Moreover, N-terminal sequence analysis of the principal phosphopeptide fragment obtained after proteolysis of the receptor yielded a sequence that corresponds to the 3 subunit of the receptor. Such data provide additional support for our hypothesis (Browning et al., 1990, Proc. Natl. Acad. Sci. USA 87:1315–1317) that both PKA and PKC phosphorylate the -subunit of the GABA_A-R.Special issue dedicated to Dr. Paul Greengard.     

Metabolism of aflatoxin, ochratoxin, zearalenone, and three trichothecenes by intact rumen fluid, rumen protozoa, and rumen bacteria

The effect of rumen microbes on six mycotoxins (aflatoxin B1, ochratoxin A, zearalenone, T-2 toxin, diacetoxyscirpenol, and deoxynivalenol ) considered to be health risks for domestic animals was investigated. The mycotoxins were incubated with intact rumen fluid or fractions of rumen protozoa and bacteria from sheep and cattle in the presence or absence of milled feed. Rumen fluid had no effect on aflatoxin B1 and deoxynivalenol . The remaining four mycotoxins were all metabolized, and protozoa were more active than bacteria. Metabolism of ochratoxin A, zearalenone, and diacetoxyscirpenol was moderately or slightly inhibited by addition of milled feed in vitro. The capacity of rumen fluid to degrade ochratoxin A decreased after feeding, but this activity was gradually restored by the next feeding time. Ochratoxin A was cleaved to ochratoxin alpha and phenylalanine; zearalenone was reduced to alpha-zearalenol and to a lesser degree to beta-zearalenol; diacetoxyscirpenol and T-2 toxin were deacetylated to monoacetoxyscirpenol and HT-2 toxin, respectively. Feeding of 5 ppm (5 mg/kg) of ochratoxin A to sheep revealed 14 ppb (14 ng/ml) of ochratoxin A and ochratoxin alpha in rumen fluid after 1 h, but neither was detected in the blood. Whether such conversions in the rumen fluid may be considered as a first line of defense against toxic compounds present in the diet is briefly discussed.     

Fanconi anemia: evidence for linkage heterogeneity on chromosome 20q

Fanconi anemia is a rare autosomal recessive disorder in which affected individuals are predisposed to acute myelogenous leukemia and other malignancies. We report the results of a genetic linkage study involving 34 families enrolled in the International Fanconi Anemia Registry. A significant lod score was obtained between D20S20, an anonymous DNA segment from chromosome 20q, and Fanconi anemia (Zmax 3.04, theta max = 0.12). However, six other anonymous DNA segments from chromosome 20q, including D20S19, which is highly polymorphic and tightly linked to D20S20, showed no or only weak evidence for linkage to Fanconi anemia. An admixture test revealed significant evidence for linkage heterogeneity (chi 2 = 6.10, P = 0.01) at the D20S19 locus. Lod scores suggestive of linkage between Fanconi anemia and this locus were obtained with two of the largest kindreds studied (lods = 2.6 and 2.1, at theta = 0.001). Thus, our data support the provisional assignment of a Fanconi anemia gene to chromosome 20q.