Prostaglandins do not mediate the actions of cholera toxin on pancreatic acini or gastric chief cells from the guinea pig

Recent reports suggest that prostaglandins, rather than cAMP, play a major role in mediating cholera toxin-induced water and electrolyte secretion from rabbit intestinal loops. We examined the role of prostaglandins in mediating toxin-induced pancreatic and gastric exocrine secretion. In these tissues, indomethacin, a potent inhibitor of prostaglandin synthesis, did not alter the stimulatory effects of cholera toxin on increases in cellular cAMP or enzyme secretion. Moreover, the addition of cholera toxin did not alter prostaglandin E2 release from either tissue. In contrast to their effects in rabbit intestinal loops, prostaglandins do not regulate cholera toxin-induced enzyme secretion from the guinea pig pancreas or stomach.     

Biochemical and genetic evidence for a macromolecular -glucuronidase complex in microsomal membranes

In the mouse β-glucuronidase is present in both microsomes and lysosomes and the enzyme at both sites is coded by the same structural gene. Electrophoresis on polyacrylamide gels showed that liver, kidney and lung from normal strains contained five enzyme forms designated L, M1, M2, M3 and M4 in order of decreasing mobility toward the anode. Band L is found primarily in lysosomes and is a tetramer of 260,000 molecular weight. Bands M1 to M4 are found exclusively in microsomes and range in molecular weight from 310,000 to 470,000. The increase in molecular weight is due to sequential addition of an accessory protein chain. When glucuronidase is highly induced in kidneys of female mice by injection of dihydrotestosterone, a sixth electrophoretic form of glucuronidase, designated X, appears. Form X appears early in induction, is localized in microsomes, and has a molecular weight (260,000) equal to that of the tetramer form L.Mice homozygous for the eg ° mutation, and thus deficient in microsomal glucuronidase, completely lack the microsomal forms M1 to M4. They do contain form X, and this increases after testosterone induction in kidney. The form X present in eg ° mice is indistinguishable from the form X seen in normal induced kidney.It appears that mice synthesize two different tetrameric forms of glucuronidase from the same structural gene. One, form L, is lysosomal; the other, form X, gives rise to microsomal enzyme forms M1 to M4 by the successive addition of up to four accessory protein chains. The eg ° mutant is blocked in the conversion of X to M1.     

Purification of hepatitis B virus gene X product synthesized in Escherichia coli and its detection in a human hepatoblastoma cell line producing hepatitis B virus

A fused gene containing 94% of the hepatitis B virus (HBV) open reading frame X was expressed in Escherichia coli, and its 17-kDa product was purified by ion-exchange chromatography. Antibody elicited against the X-gene product reacted with materials proximal to the nuclear membrane of a human hepatoblastoma cell line producing HBV particles. No such reaction was observed with the same cell line that did not produce HBV particles.     

Identification of the coding region for the putidaredoxin reductase gene from the plasmid of Pseudomonas putida

The first 12 NH₂-terminal amino acids of the Pseudomonas putida putidaredoxin reductase were shown to be Met-Asn-Ala-Asn-Asp-Asn-Val-Val-Ile-Val-Gly-Thr. Comparison of these data with the DNA sequence of the BamHI-HindIII 197-base fragment derived from the PstI 2.2-kb fragment obtained from the P. putida plasmid showed that the putidaredoxin reductase gene was downstream from the cytochrome P-450 gene and the intergenic region had the 24-nucleotide sequence TAAACACATGGGAGTGCGTGCTAA. The Shine-Dalgarno sequence GGAG was detected in this region. The initiating triplet for the reductase gene was GTG, which normally codes for valine, but in the initiating codon position codes for methionine. From the amino acid sequence and X-ray data comparisons with other flavoproteins, what appears to be the AMP binding region of the FAD can be recognized in the NH₂-terminal portion of the reductase involving residues 5–35.This article was presented during the proceedings of the International Conference on Macromolecular Structure and Function, held at the National Defence Medical College, Tokorozawa, Japan, December 1985.     

Early events in the life of apple roots: variation in root growth rate is linked to mycorrhizal and nonmycorrhizal fungal colonization

Early events of mycorrhizal and nonmycorrhizal fungal colonization in newly-emerging roots of mature apple (Malus domestica Borkh) trees were characterized to determine the relationship of these events to fine root growth rate and development. New roots were traced on root windows to measure growth and then collected and stained to quantify microscopically the presence of mycorrhizal and nonmycorrhizal fungal structures. Most new roots were colonized by either mycorrhizal or nonmycorrhizal fungi but none less 25 days old were ever internally colonized by both. Compared to nonmycorrhizal colonization, mycorrhizal colonization was associated with faster growing roots and roots that grew for a longer duration, leading to longer roots. While either type of fungi was observed in roots as soon as 3 days after root emergence, intraradical colonization by mycorrhizal fungi was generally faster (peaking at 7 to 15 days) than that by nonmycorrhizal fungi and often occurred more frequently in younger roots. Only 15 to 35% of the roots had no fungal colonization by 30 days after emergence. This study provides the first detailed examination of the early daily events of mycorrhizal and nonmycorrhizal fungal colonization in newly emerging roots under field conditions. We observed marked discrimination of roots between mycorrhizal and nonmycorrhizal fungi and provide evidence that mycorrhizal fungi may select for faster growing roots and possibly influence the duration of root growth by non-nutritional means.