Hormonal requirements for the induction of cytochrome P-450 in hepatocytes cultured in a serum-free medium

Drug mediated induction of cytochrome P450 was studied in cultures of hepatocytes that had never been cultured in the presence of serum. Propylisopropylacetamide induced a five-fold increase in cytochrome P450, approximating $\text{in ovo}$ induced levels, when triiodothyronine and/or dexamethasone were included in the culture medium. Insulin was apparently not required for this induction. Cytochrome P450, free of cytochrome oxidase, could be fully recovered from cell homogenates in a 8700g supernatant, by use of a buffer containing 0.2% Emulgen.     

Formation of cobalt protoporphyrin in the liver of rats. A mechanism for the inhibition of liver haem biosynthesis by inorganic cobalt.

1. Treatment of rats with small doses of CoCl2 decreases liver 5-aminolaevulinate synthase (EC 2.3.1.37) activity and impairs incorporation of 5-amino[14C]laevulinate into liver haem. Salts of other metals (cadmium, nickel, manganese and zinc) are all relatively inactive. 2. The dose-response curves obtained for both these effects closely mirror the accumulation in the liver of a compound that is labelled by 5-amino[14C]laevulinate and is unextractable by acetone/HCl. 3. Incorporation of 5-amino[14C]laevulinate into unextractable compound is also obtained in vitro by incubating liver homogenates with label in the presence of cobalt:isotope-dilution experiments show that the radioactivity passes through pools of porphobilinogen and protoporphyrin, but not of haem. 4. The unextractable compound is not covalently bound to protein and possesses the same extraction and spectral properties as authentic cobalt protoporphyrin. 5. It is concluded (a) that cobalt protoporphyrin is readily formed not only in vitro, but also in vivo, and (b) that its formation accounts for the impaired incorporation of 5-aminolaevulinate into haem and may also be responsible for the action of cobalt on 5-aminolaevulinate synthase.     

Blood-pressure screening and supervision in general practice.

Since April 1975 all men aged 35-69 years registered with four general practices in west central Scotland have had their blood pressure checked whenever they visit the surgery. Although the practice locations range from rural to city centre and observers comprise receptionists, nurses, and doctors, a standard procedure has been adopted for the examination, recording, follow-up, and management of high blood pressure. The results confirm that raised blood pressure is common and often goes undetected. Even when hypertension is known, casual blood pressure readings often exceed accepted normal levels. The findings also show that a population may be routinely examined through normal contact with the family doctor, and that this can provide a convenient, acceptable, and effective means of detecting and reducing raised blood pressure.     

Properties of the low-temperature Photosystem I primary reaction in the P-700-chlorophyll a-protein

The Photosystem I primary reaction, as measured by electron paramagnetic resonance changes of P-700 and a bound iron-sulfur center, has been studied at 15°K in P-700-chlorophyll a-protein complexes isolated from a blue-green alga. One complex, prepared with sodium dodecyl sulfate shows P-700 photooxidation only at 300°K, whereas a second complex, prepared with Triton X-100, is photochemically active at 15°K as well as at 300°K. Analysis of these two preparations shows that the absence of low-temperature photoactivity in the sodium dodecyl sulfate complex reflects a lack of bound iron-sulfur centers in this preparation and supports the assignment of an iron-sulfur center as the primary electron acceptor of Photosystem I.     

Models for the continuous culture of microorganisms under both oxygen and carbon limiting conditions

Two models for predicting the behavior of cultures of microorganisms under both oxygen and carbon limiting conditions have been evlauated on a chemostat growing Candida utilis on a glycolysis suppressing glycerol medium. The work indicated that parameter values obtained under wholly oxygen limiting or wholly carbon limiting conditions successfully predict the behavior of the chemostat under the wide range of flow and substrate concentration conditions tested. Both models are satisfactory and hence it is deduced that the simpler one may be used with confidence. It was found that Monod kinetics were applicable to the growth rate dependence on oxygen concentration but that Contois kinetics were superior for the corresponding dependence on carbon substrate concentration.     

Intraspecific Variation of Ribosomal Gene Redundancy in ZEA MAYS

Ribosomal genes in eukaryotes are highly redundant. Considerable variation in the level of redundancy among species, especially in higher plants, has been reported; but except for deletion and duplication mutants, it is generally accepted that intraspecific variability in redundancy level is small. We have examined the level of redundancy in several lines of maize by DNA-rRNA saturation hybridization. The amount of nuclear DNA which hybridizes with rRNA in the ten lines examined varied from 0.24% to 0.50%. The number of rRNA genes per diploid genome thus ranges from 1.12 x 10⁴ to 2.32 x 10⁴. Results also indicate that the level of redundancy is genetically transmitted.     

The complexity of satellite deoxyribonucleic acid in a higher plant.

Purified satellite DNA from melon (Cucumis melo) was shown to contain at least two components from thermal-denaturation and renaturation studies. Two components were separated after partial renaturation, a fast-renaturing fraction similar in complexity to mouse satellite DNA, and one with 6000 times greater complexity. Both components renatured very accurately, indicating a minimum of sequence divergence. Centrifugation of the purified satellite DNA in Ag+/Cs2SO4 gradients resolved two major and several minor fractions. The two major fractions were only slightly enriched for fast- or slow-renaturing sequences.