Computer control for continuous cultivation ofSaccharomyces cerevisiae

Summary An on-line respiratory quotient control system has been developed for the continuous cultivation of baker's yeast. This system is based on moving identification of the microbial dynamics. The optimal dilution rate that was selected as the control variable was determined by minimizing a performance index. Without resorting to complicated microbial analysis, a simple and practical moving model is obtained by continually updating the input and output data. The experimental results indicate the satisfactory controllability of the present system and the possible extention of the proposed method to other bioprocesses.     

Vitamin C partially reversed some biochemical changes produced by vitamin E deficiency

Feeding a basal diet free of vitamins E and C to weanling male rats for 8 months resulted in biochemical changes characteristic of vitamin E deficiency. These included increased liver thiobarbituric acid values; decreased blood GSH levels, plasma vitamin E levels, and glutathione peroxidase activities; and increased activities of plasma pyruvate kinase, glutamic-oxaloacetic transaminase, creatine kinase, lactic dehydrogenase, and malic dehydrogenase. Tube-feeding vitamin C for 21 days resulted in partial reversal effects on the above parameters except activities of glutathione peroxidase, lactic dehydrogenase, and malic dehydrogenase. The results suggest that vitamin C may spare in part the metabolism of vitamin E through its antioxidant property.     

Differences in chromatin from normal and leukemic human cells as shown by digestion with restriction nucleases

Sequence homology was found by computer analysis between potato spindle tuber viroid (PSTV) RNA and U3B snRNA of Novikoff hepatoma cells. This homology is colinear in arrangement, extends in length to 81% of the entire U3B snRNA molecule and is involved in the PSTV molecule unique sites which, if depicted in terms of the secondary structure of the circular PSTV molecule, reveal a conspicuous regularity in their location. A strong relation in primary structure between PSTV and U3B snRNA is demonstrated by statistical analysis.     

Increase in brain 125I-cholecystokinin (CCK) receptor binding following chronic haloperidol treatment, intracisternal 6-hydroxydopamine or ventral tegmental lesions

Specific 125I-CCK receptor binding was significantly increased in brain tissue taken from guinea pig or mouse following chronic (2-3 week) daily administration of haloperidol (2-3 mg/kg/day). Scatchard analysis indicated the increase in CCK binding was due to an increased receptor number (B max) with no change in affinity (Kd). In guinea pigs, the increased CCK binding was observed in the mesolimbic regions and frontal cortex, but not in striatum, hippocampus nor posterior cortex. In mice, however, the increases occurred in both pooled cerebral cortical-hippocampal tissue, and in the remainder of the brain. Enhanced CCK receptor binding was also observed in membranes prepared from whole brain of mice one month following intracisternal injection of 6-hydroxydopamine. Additionally, an increase in CCK binding was observed in mesolimbic regions and frontal cortex, but not striatum or hippocampus, of guinea pigs 3 weeks after an unilateral radiofrequency lesions of the ipsilateral ventral tegmentum. The present studies demonstrate that three different procedures which reduce dopaminergic function in the brain enhance CCK receptor binding. The data provide further support for a functional interrelationship between dopaminergic systems and CCK in some brain regions and raise the possibility that CCK may play a role in the antipsychotic action of neuroleptics.     

An age dependent stochastic model of periodic screening: Basic properties

An age dependent stochastic model for the periodic screening of a progressive chronic disease is developed in this paper by combining results from previous modeling efforts. The basic concepts used are the random variables describing the disease free state and preclinical state sojourn times and the age at screening or observation, as well as generations of individuals defined according to time of entry into the preclinical state. At discrete time points, the model characterizes the density functions for individuals who are healthy, have preclinical disease, or have clinical disease. The joint density functions of age and sojourn times for cases detected by a periodic screening program and for cases which surface clinically between screens are derived as functions of screening interval, false negative rate, and disease natural history.     

A modified method of UDS detection in vitro suitable for screening the DNA-damaging effects of chemicals

The UDS induced in cultured FL cells by exposure to chemicals was measured as hydroxyurea-resistant incorporation of 3H-TdR in the acid-insoluble fraction of the 14C-TdR-prelabelled cells synchronized by the combination of arginine starvation and pretreatment with hydroxyurea. The level of UDS is represented by the ratios of 3H/14C radioactivities which are measures of specific activities of 3H. Two direct-acting alkylating agents, MMS and MNNG, a cross-linking agent, mitomycin C, and 3 procarcinogens, B(a)P, AFB1 and cyclophosphamide elicited UDS in the absence or presence of the liver-metabolizing system. Three chemicals of unknown carcinogenicity were also able to induce UDS in this assay system, i.e., bis-(O,O-diethylphosphinothioyl)-disulphide, 4-chlorophenoxy acetic acid (sodium salt) and caramelized malt sugar. With the exception of 4-chlorophenoxy acetic acid, they were also active in the Ames test.     

Tumor-promoting phorbol esters inhibit the binding of colony-stimulating factor (CSF-1) to murine peritoneal exudate macrophages

L-cell colony-stimulating factor (CSF-1) is a sialoglycoprotein of molecular weight 70,000 daltons that specifically stimulates macrophage colony formation by single committed cells from normal mouse bone marrow and by various classes of more differentiated tissue-derived mononuclear phagocyte colony-forming cells (Stanley et al., 1978). CSF-1 interacts with target cells by direct and specific binding to membrane receptors (CSF-1 receptors) that are present only on cells of the mononuclear phagocyte series and their precursors. We studied the effect of tumor-promoting phorbol esters on the binding of 125I-labeled CSF-1 (125I-CSF-1) to murine peritoneal exudate macrophages (PEM). Biologically active TPA (12-O-tetradecanoyl phorbol-13-acetate) inhibits the binding of 125I-CSF-1 to its receptor on PEM. This inhibition exhibits temperature, time, and concentration dependence. At 37 degrees C, maximum inhibition occurred at about 10(-7) M; inhibition was 50% at 5 X 10(-9) M. At 0 degrees C, the inhibitory activity of TPA is diminished. The action of TPA on PEM is transient. Treated cells recover their 125I-CSF-1-binding activity whether TPA is later removed or not. The process of recovering CSF-1-binding activity is completely blocked by the addition of cycloheximide. When several phorbol derivatives were tested for their inhibitory activities, only biologically active phorbol esters were found to possess such activities. Furthermore, the inhibitory activities of various phorbol esters are proportional to their tumor-promoting activities. Inhibition appears to be due to a reduction in the total number of available CSF-1 receptors rather than a decrease in receptor affinity.     

Refined 2 A X-ray crystal structure of porcine pancreatic kallikrein A, a specific trypsin-like serine proteinase. Crystallization, structure determination, crystallographic refinement, structure and its comparison with bovine trypsin

Porcine pancreas kallikrein A has been crystallized in the presence of the small inhibitor benzamidine, yielding tetragonal crystals of space group P4₁2₁2 containing two molecules per asymmetric unit. X-ray data up to 2·05 Å resolution have been collected using normal rotation anode as well as synchrotron radiation. The crystal structure of benzamidine-kallikrein has been determined using multiple isomorphous replacement techniques, and has subsequently been refined to a crystallographic R-value of 0·220 by applying a diagonal matrix least-squares energy constraint refinement procedure.Both crystallographically independent kallikrein molecules 1 and 2 are related by a non-integral screw axis and form open, heterologous “dimer” structures. The root-mean-square deviation of both molecules is 0·37 Å for all main-chain atoms. This value is above the estimated mean positional error of about 0·2 Å and reflects some significant conformational differences, especially at surface loops. The binding site of molecule 1 in the asymmetric unit is in contact with residues of molecule 2, whereas the binding site of the latter is free and accessible to the solvent. In both molecules the characteristic “kallikrein loop”, where the peptide chain of kallikrein A is cleaved, is only partially traceable. The carbohydrate attached to Asn95 in this loop, although detectable chemically, is not defined.A comparison of the refined structures of porcine kallikrein and bovine trypsin indicates spatial homology for these enzymes. The root-mean-square difference is 0·68 Å if we compare only main-chain atoms of internal segments. Remarkably large deviations are found in some external loops most of which surround the binding site and form a more compact rampart around it in kallikrein than in trypsin. This feature might explain the strongly reduced activity and accessibility of kallikrein towards large protein substrates and inhibitors (e.g. as shown by the model-building experiments on inhibitor complexes reported by Chen &; Bode. 1983).The conformation of the active site residues is very similar in both enzymes. Tyr99 of kallikrein, which is a leucyl residue in trypsin, protrudes into the binding site and interferes with the binding of peptide substrates (Chen &; Bode. 1983). The kallikrein specificity pocket is significantly enlarged compared with trypsin due to a longer peptide segment, 217 to 220, and to the unique outwards orientation of the carbonyl group of cis-Pro219. Further, the side-chain of Ser226 in porcine kallikrein, which is a glycyl residue in trypsin, partially covers Asp 189 at the bottom of the pocket. These features considerably affect the binding geometry and strength of binding of benzamidine.     

The genes coding for 4 snRNAs of Drosophila melanogaster: localization and determination of gene numbers.

Four small nuclear RNAs (snRNAs) have been isolated from Drosophila melanogaster flies. They have been characterized by base analysis, fingerprinting, and injection into Axolotl oocytes. The size of the molecules and the modified base composition suggest that the following correlations can be made: snRNA1 approximately U2-snRNA; snRNA2 approximately U3-snRNA; snRNA3 approximately U4-snRNA; snRNA4 approximately U6-snRNA. The snRNAs injected into Axolotl oocytes move into the nuclei, where they are protected from degradation. The genes coding for these snRNAs have been localized by "in situ" hybridization of 125-I-snRNAs to salivary gland chromosomes. Most of the snRNAs hybridize to different regions of the genome: snRNA1 to the cytological regions 39B and 40AB; snRNA2 to 22A, 82E, and 95C; snRNA3 to 14B, 23D, 34A, 35EF, 39B, and 63A; snRNA4 to 96A. The estimated gene numbers (Southern-blot analysis) are: snRNA1:3; snRNA2:7; snRNA3:7; snRNA4:1-3. The gene numbers correspond to the number of sites labeled on the polytene salivary gland chromosomes.