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71.
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73.
Two crude fractions of acid-resistant trypsin inhibitors (apparent molecular masses 44 and 20 kDa, respectively) were prepared from human urine by gel permeation chromatography. From both preparations the pure inhibitors were isolated by high performance liquid chromatography (HPLC). Their N-terminal amino-acid sequences were determined and compared with those of HI-30 and HI-14 as isolated by reversible binding to either immobilized trypsin or immobilized chymotrypsin. The N-terminal amino-acid sequence of the high-molecular mass inhibitor UI-I isolated by HPLC was identical with those of HI-30 and UI-C-I isolated via immobilized trypsin or chymotrypsin, respectively. The low-molecular mass inhibitors UI-II and UI-C-II differ from HI-14 by the N-terminal extension Glu-Val-Thr-Lys-when obtained by HPLC or by the extension Thr-Lys-when obtained via immobilized chymotrypsin, respectively. The comparison of these N-termini with the amino-acid sequence of HI-30 (Ala1-...-Val16-Thr-Glu-Val-Thr-Lys-HI-14) defines the low molecular urinary trypsin inhibitors as proteolytic degradation products of the high-molecular urinary inhibitor. Proteolysis may occur at different bonds. The existing discrepancies in molecular architecture and in molecular masses of the urinary trypsin inhibitors are discussed.  相似文献   
74.
Stilbene synthase ( resveratrol -forming) converts one molecule of rho- coumaroyl -CoA and three molecules of malonyl-CoA into 3,4',5- trihydroxystilbene . Following selective induction of stilbene synthesis in cell suspension cultures of peanut (Arachis hypogaea), the enzyme was extracted and purified to apparent homogeneity by chromatography on DEAE-cellulose and hydroxylapatite. The enzyme was found to be a dimer of estimated Mr = 90,000 exhibiting under denaturing conditions a subunit Mr of approximately 45,000. The isoelectric point was determined with pI = 4.8. The enzyme's high selectivity towards rho- coumaroyl -CoA (Km = 2 microM) as substrate qualified it as resveratrol -forming stilbene synthase. Structurally related CoA esters, e.g. dihydro-rho- coumaroyl -CoA and cinnamoyl-CoA, were converted less than 1/10 as efficiently as rho- coumaroyl -CoA. Malonyl-CoA (Km = 10 microM) could not be substituted by acetyl-CoA. The purified enzyme was free of chalcone synthase activity. Antibodies raised against stilbene synthase were shown to be monospecific and not to cross-react with chalcone synthase.  相似文献   
75.
Cytoskeletal filaments of the α-keratin type (cytokeratins) are a characteristic of epithelial cells. In diverse mammals (man, cow and rodents) these cytokeratins consist of a family of approximately 20 polypeptides, which may be divided into the more acidic (I) and the more basic (II) subfamilies. These two subfamilies show only limited amino acid sequence homology. In contrast, nucleic acid hybridization experiments and peptide maps have been interpreted to show that polypeptides of the same subfamily share extended sequence homology.We compare two polypeptides of the acidic cytokeratin subfamily, VIb (Mr 54,000) and VII (Mr 50,000), which are co-expressed in large amounts in bovine epidermal keratinocytes. These two epidermal keratins can be distinguished by specific antibodies and show different patterns of expression among several bovine tissues and cultured cells. In addition, they differ in the stability of their complexes with basic keratin polypeptides and in their tryptic peptide maps. The amino acid sequences deduced from the nucleotide sequences of complementary DNA clones containing the 3′ ends of the messenger RNAs for these keratins are compared with each other and with available amino acid sequences of human, murine and amphibian epidermal keratins. Bovine keratins VIb and VII share considerable sequence homology in the α-helical portion (68% residues identical) but lack significant homology in the extrahelical portion. Bovine keratin VIb shows, in its α-helical region, a pronounced sequence homology (88% identity) to the murine epidermal keratin of Mr 59,000. In addition, the non-helical carboxy-terminal regions of both proteins are glycinerich and contain a canonic sequence GGGSGYGG, which may be repeated several times. Moreover, their mRNAs present a highly conserved stretch of 236 nucleotides containing, in the murine sequence, the end of the coding and all of the non-coding region (81% identical nucleotides). Bovine keratin VII is considerably different from the murine Mr 59,000 keratin but is almost identical to the human cytokeratin number 14 of Mr 50,000, both in the α-helical and in the non-α-helical regions of the proteins, and the mRNAs of the human and the bovine keratins also display a high homology in their 3′ non-coding ends.The results show that in the same species keratins of the same subfamily can differ considerably, whereas equivalent keratin polypeptides of different species are readily identified by characteristic sequence homologies in the α-helical and the non-helical regions as well as in the 3′ non-coding portions of their mRNAs. Among the members of the acidic subfamily I of cytokeratin polypeptides that are co-expressed in bovine epidermis, at least two types can be distinguished by their carboxy-terminal sequences. One type is characterized by its abundance of glycine residues, a consensus GGGSGYGG heptapeptide sequence, which may be repeated several times, and an extended stretch of high RNA sequence homology in the 3′ non-coding part. The other type shows a predominance of serine and valine residues, a subterminal GGGSGYGG sequence (which has been maintained in Xenopus, cow and man) and also a high level of homology in the 3′ non-coding part of the mRNA. The data indicate that individual keratin type specificity overrides species diversity, both at the protein and the mRNA level. We discuss the evolutionary conservation and the tissue distribution of these two types of acidic keratin polypeptides as well as their possible biological functions.  相似文献   
76.
Enzyme production with E. coli ATCC 11105, in a complex medium using phenylacetic acid as inducer is carried out in a stirred-tank reactor of 10 dm3 and an airlift tower-loop reactor of 60 dm3 with outer loop at a temperature of 27 °C. The optimum inducer concentration was 0.8 kg/m3, which was kept constant by fed-batch operation. The optimum of the relative dissolved O2-concentration with regard to saturation is below 10% in a stirred-tank reactor and at 35% in a tower-loop reactor. It was kept constant by parameter-adaptive control of the aeration rate. In a stirred-tank enzyme productivity is slightly higher than in a tower-loop reactor, and much higher than in a bubble column reactor.List of Symbols CPR kg/(m3 h) CO2-production rate - OTR kg/(m3 h) O2-transfer rate - OUR kg/(m3 h) O2-utilization rate - PAA phenylacetic acid (inducer) - RQ = CPR/OUR respiratory quotient - X kg/m3 cell mass concentration - m h–1 maximum specific growth rate  相似文献   
77.
E. coli ATCC 11105 was cultivated in a 10-1 stirred tank reactor and in a 60-1 tower loop reactor in batch and continuous operation. By on-line measurements of O2 and CO2 concentrations in the outlet gas, pH, temperature, cell mass concentration X as well as dissolved O2 concentration along the tower in the broth, gas holdup, broth recirculation rate through the loop and by offline measurements of substrate concentration DOC and cell mass concentration along the tower, the maximum specific growth rate m , yield coefficients Y X/S. Y X/DOC and were evaluated in stirred tank and tower loop in batch and continuous cultures with and without motionless mixers in the tower and at different broth circulation rates through the loop. To control the accuracy of the measurements the C balance was calculated and 95% of the C content was covered.The biological parameters determined depend on the mode of operation as well as on the reactor used. Furthermore, they depend on the recirculation rate of the broth and built-ins in the tower. The unstructured cell and reactor models are unable to explain these differences. Obviously, structured cell and reactor models are needed. The cell mass concentration can be determined on line by NADH fluorescence in balanced growth, if the model parameters are determined under the same operational conditions in the same reactor.List of Symbols a, b empirical parameters in Eq. (1) - CPR kg/(m3 h) CO2 production rate - C kg/m3 concentration - D l/h dilution rate - DOC kg/m3 dissolved organic carbon - I net. fluorescence intensity - K S kg/m3 Monod constant - k L a l/h volumetric mass transfer coefficient - OTR kg/(m3 h) oxygen transfer rate - OUR kg/(m3 h) oxygen utilization rate - RQ = CPR/OUR respiratory quotient - S kg/m3 substrate concentration - t h,min, s time - t u min recirculation time - t M min mixing time - v m3/h volumetric flow rate through the loop - X kg/m3 (dry) cell mass concentration - Y X/S yield coefficient of cell mass with regard to the consumed substrate - Y X/DOC yield coefficient of the cell mass with regard to the consumed DOC - Y X/O yield coefficient of the cell mass with regard to the consumed oxygen - Z relative distance in the tower from the aerator with regard to the height of the aerated broth - l/h specific growth rate - m l/h maximum specific growth rate Indices f feed - e outlet  相似文献   
78.
We assume that the mammalian neocortex is built up out of some six layers which differ in their morphology and their external connections. Intrinsic connectivity is largely excitatory, leading to a considerable amount of positive feedback. The majority of cortical neurons can be divided into two main classes: the pyramidal cells, which are said to be excitatory, and local cells (most notably the non-spiny stellate cells), which are said to be inhibitory. The form of the dendritic and axonal arborizations of both groups is discussed in detail. This results in a simplified model of the cortex as a stack of six layers with mutual connections determined by the principles of fibre anatomy. This stack can be treated as a multi-input-multi-output system by means of the linear systems theory of homogeneous layers. The detailed equations for the simulation are derived in the Appendix. The results of the simulations show that the temporal and spatial behaviour of an excitation distribution cannot be treated separately. Further, they indicate specific processing in the different layers and some independence from details of wiring. Finally, the simulation results are applied to the theory of visual receptive fields. This yields some insight into the mechanisms possibly underlying hypercomplexity, putative nonlinearities, lateral inhibition, oscillating cell responses, and velocity-dependent tuning curves.  相似文献   
79.
Recent field data indicate that MacKinnon’s model of the orang-utan’s sexual and agonistic activity needs to be revised. In this model, male reproductive activity is concentrated in an extended phase of subadulthood and in early adulthood. According to this model, the role of older adult males is primarily that of range guardian, and in that role they would ensure that the offspring they had generated earlier would have safe access to food resources. This study presents cases suggesting that subadult males, even though sexually active, may have low reproductive success. In previous studies adult males were shown to display less sexual initiative than subadult males. In this study an adult male was at times involved infrequent mating activity in response to proceptive activity of females in the course of consortship. This adult male proved to be a successful breeder, thus refuting the hypothesis of adult male sterility. The female is most likely to conceive through cooperative mating in lengthy consortships with the dominant resident adult male. We hypothesize that the extended subadult phase represents a submissive strategy, allowing subadult males to remain in the home range of adult males but with minimal reproductive success.  相似文献   
80.
Transmitter glutamate/aspartate synthesis is known to proceed along different metabolic pathways. In this light, the functional relevance of glutamate dehydrogenase in postnatally maturing glutamatergic/aspartatergic structures was studied by means of quantitative enzyme histochemistry. The basic requirements concerning the kinetics and calibration of the histochemical glutamate dehydrogenase reaction used were proved to be met in order to obtain valid quantitative data. The histochemically demonstrable activity of glutamate dehydrogenase (EC 1.4.1.3) in the hippocampal formation of the rat increased markedly during postnatal development. On day 30, the distribution pattern observed was similar to that in adult animals. While the enzyme activity rose within cell body layers from day 0 to day 30 by 240-285%, the increase in neuropil layers was found to be up to 830%. Maximum values were seen in the stratum lacunosum-moleculare of CA1 and CA3 and the stratum moleculare of the dentate fascia on day 30. Since the hippocampal neuropil is supposed to be copiously provided with glutamatergic (and aspartatergic?) structures which become functional in rats during the first weeks of postnatal life, the increase in enzyme activity is discussed to be primarily a consequence of maturing synaptic systems using glutamate and/or aspartate as transmitters.  相似文献   
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