Correlation of changes in pineal gland cAMP metabolism with light-mediated decrease in N-acetyltransferase activity

The present study investigated the correlation between the light-mediated decrease in rat pineal N-acetyltransferase (NAT) observed in vivo and changes in cAMP metabolism. While exposing dark-adapted rats to light for short time periods (0–10 min) resulted in a rapid decrease in pineal NAT activity, cAMP exhibited a biphasic response. Following light exposure for 30 s there was a 50% decrease in cAMP levels. However, after 6 min of light exposure the cyclic nucleotide levels had increased 2–3 times above control values. These responses were prevented by phenoxybenzamine pretreatment and the initial decrease was mimicked by i.v. propranolol administration. Examination of cAMP metabolic enzymes, adenylate cyclase and phosphodiesterase revealed an increase in adenylate cyclase activity following 6 min of exposure to light. We discussed how the results observed in vivo compare with those observed using cultured pinealocytes.     

Ascorbic acid accumulation by cultured rat adrenocortical cells

Summary The influence of adrenocorticotrophin (ACTH) on radiolabeled ascorbic acid (AA) accumulation by adrenocortical cells was examined in primary cultures of collagenase dissociated glands from adult male rats. The cells were ACTH responsive by morphological and steroidogenic criteria. After 5 d in AA-free medium, cells pretreated with 100 mU/ml ACTH for 3 d took up two to three times more AA over a 2 h period than did untreated controls (4.0 to 10.0 nmol versus 1.7 to 3.4 nmol AA/μg DNA). In contrast, ACTH administered on Day 6 concurrently with AA inhibited AA accumulation compared to cultures exposed to AA alone. This acute inhibitory effect of ACTH was in the order of 30% in cultures pretreated with ACTH for 3 d but was not significant (7%) without ACTH pretreatment. The results show that ACTH has distinct long term stimulatory and acute inhibitory effects on AA accumulation by adrenocortical cells and suggest that both maximal AA accumulation and the responsiveness to acute inhibition of AA accumulation by ACTH may depend on the maintenance of the differentiated state of the adrenal cortex. This work was supported by a grant and research associateship to N. A. from the National Cancer Institute of Canada.     

Properties of a partially-purified preparation of the prostaglandin-forming oxygenase from sheep vesicular gland

The fatty acid oxygenase of sheep vesicular glands was solubilized with Tween-40 and purified 60-fold using ammonium sulfate precipitation and DEAE-cellulose chromatography. Glycerol (50%) stabilized the activity at all stages of purification and allowed long-term storage at −60°. The partially purified enzyme contained less than 0.7 nmoles of iron per mg of protein and less than 0.1 nmole of copper per mg of protein. Although the K_I values for aspirin, BL-2338, flurbiprofen and ibuprofen remained relatively unchanged during purification, the apparent K_I value for inhibition by indomethacin decreased from 120 to 2.7 μ$\text{M}$.     

Susceptibility of Freshly Picked Ear Corn to Invasion by Fungi

High-moisture ear corn held 9 days at 23 C remained free of visible mold or evidence of Aspergillus flavus invasion provided there was no mechanical damage of the kernels.     

Protein synthesis in the cotyledons of Pisum sativum L. Protein factors involved in the binding of phenylalanyl-transfer ribonucleic acid to ribosomes

1. Proteinaceous factors contained in a 0.5m-KCl extract of ribosomes from pea cotyledons form a ternary complex at 0 degrees C with [(14)C]phenylalanyl-tRNA and poly(U). The complex is measured by its quantitative retention on Millipore filters. 2. Complex-assembly is optimal at 5mm-Mg(2+) and is independent of GTP and ribosomes. 3. The addition of ribosomes is required to stabilize the complex at 34 degrees C. The complex binds to a puromycin-sensitive site on the ribosome. 4. Soluble factors from the 250000g supernatant of pea cotyledon form a Millipore-retainable complex dependent on GTP and ribosomes. 5. Complex-formation by soluble factors has a Mg(2+) optimum of 10-12mm and forms a puromycin-insensitive complex with ribosomes. 6. The function of the ribosomal protein factors and the supernatant fraction in initiation of protein synthesis is discussed.     

Early Events in Development of Streptococcal Competence

Appropriately timed use of trypsin, which inactivates competence factor (CF), and chloramphenicol made feasible a separation and characterization of early events in the development of competence in group H streptococci. Step 1 is production of CF, which is inseparable in time from the concomitant release of free CF into the medium. The producing cells, which are noncompetent at the time, also accumulate cell-bound CF (CB-CF) from the onset of CF synthesis. In step 2, the released CF is adsorbed or taken up in a trypsin-insensitive state by the producing cells and is not destroyed as previously suggested. This occurs rapidly in a transformation-supporting (complete) medium. The rapid decline in free CF is concomitant with the rise in CB-CF, and a maximal increase in the latter does not occur in cultures exposed to trypsin, which inactivates any trypsin-accessible CF. The rapid increase in CB-CF (above trypsin-treated levels) leads to step 3, the induction of competence. All of these steps probably require protein synthesis, because each is inhibited by chloramphenicol. The data also indicate that only free CF that is subsequently adsorbed, and which thus leads to maximal levels of trypsin-insensitive CB-CF, is the effective inducer of competence in either CF-producing (Challis) or CF-nonproducing (Wicky) cultures. The processes induced by the newly bound CF are not fully understood, but certain new properties, previously described by others as indicating competence, were measured during the several steps of competence development. Cell aggregation at pH 2 appears to be related to CB-CF and can be shown before this bound CF has induced competence. The ability of cultures to autolyze maximally can be diminished by trypsin treatment of precompetent cells without affecting subsequent competence development as measured by transformation.