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101.
1. The properties of pyruvate kinase and, if present, phosphoenolpyruvate carboxykinase from the muscles of the sea anemone, scallop, oyster, crab, lobster and frog were investigated. 2. In general, the properties of pyruvate kinase from all muscles were similar, except for those of the enzyme from the oyster (adductor muscle); the pH optima were between 7.1 and 7.4, whereas that for oyster was 8.2; fructose bisphosphate lowered the optimum pH of the oyster enzyme from 8.2 to 7.1, but it had no effect on the enzymes from other muscles. Hill coefficients for the effect of the concentration of phosphoenolpyruvate were close to unity in the absence of added alanine for the enzymes from all muscles except oyster adductor muscle; it was 1.5 for this enzyme. Alanine inhibited the enzyme from all muscles except the frog; this inhibition was relieved by fructose bisphosphate. Low concentrations of alanine were very effective with the enzyme from the oyster (50% inhibition was observed at 0.4mm). Fructose bisphosphate activated the enzyme from all muscles, but extremely low concentrations were effective with the oyster enzyme (0.13mum produced 50% activation). 3. In general, the properties of phosphoenolpyruvate carboxykinase from the sea anemone and oyster muscles are similar: the K(m) values for phosphoenolpyruvate are low (0.10 and 0.13mm); the enzymes require Mn(2+) in addition to Mg(2+) for activity; and ITP inhibits the enzymes and the inhibition is relieved by alanine. These latter compounds had no effect on enzymes from other muscles. 4. It is suggested that changes in concentrations of fructose bisphosphate, alanine and ITP produce a coordinated mechanism of control of the activities of pyruvate kinase and phosphoenolpyruvate carboxykinase in the sea anemone and oyster muscles, which ensures that phosphoenolpyruvate is converted into oxaloacetate and then into succinate in these muscles under anaerobic conditions. 5. It is suggested that in the muscles of the crab, lobster and frog, phosphoenolpyruvate carboxykinase catalyses the conversion of oxaloacetate into phosphoenolpyruvate. This may be part of a pathway for the oxidation of some amino acids in these muscles. 相似文献
102.
Eric Jakobsson 《Journal of mathematical biology》1978,6(3):235-248
Summary The axon membrane is simulated by standard Hodgkin-Huxley leakage and potassium channels plus a coupled transient excited
state kinetic scheme for the sodium channel. This scheme for the sodium channel is as proposed previously by the author. Simultations
are presented showing the form of the action potential, threshold behavior, accommodation, and repetitive firing. It is seen
that the form of the individual action potential, its all-or-none nature, and its refractory period are well simulated by
this model, as they are by the standard Hodgkin-Huxley model. However, the model differs markedly from the Hodgkin-Huxley
model with respect to repetitive firing and accommodation to stimulating currents of slowly rising intensity, in ways that
are anomn to be related to those features of the sodium inactivation which are anomalous to the H-H model. The tendency for
repetitive firing is highly dependent on that parameter which primarily determintes the existence of the inactivation shift
in voltage clamp experiments, in such a way that the more pronounced the inactivation shift, the less the tendency for repetitive
firing,. The tendency for accommodation is highly dependent on that parameter which primarily determines the “τc − τh” separation, in such a way that the greater the separation the greater the tendency for the membrane to accommodate without
firing action potentials to a slowly rising current. 相似文献
103.
The fat body of developing mid- and late fourth instar larvae of a midge, Chironomus thummi, has been investigated by means of the benzidine reaction for the localization of haemoglobin within cells. In the subepidermal fat body the reaction deposits of the haemoglobin pseudo-peroxidase activity appear predominantly in the intracisternal cavities of ER and the Golgi, and later, in the pharate pupal stage, in small dense granules (0.5–1 μm in. diameter).All the major protein bands of fat body extracts, which are resolved in electrophoresis, give the benzidine reaction and show incorporation of 14C-amino levulinic acids, in this case a specific marker for haemoglobin synthesis. In addition, labelled proteins show identical electrophoretic mobility as the haemoglobins of the haemolymph, suggesting that haemoglobins are synthesized in the fat body. Two types of fat body cells seem to differ with respect to their rôle in haemoglobin metabolism. 相似文献
104.
105.
Lymphocytes from chickens homozygous (B
2
B
2) at the major histocompatibility complex (MHC) were tested for cytotoxic activity against five types of target chicken embryo fibroblasts (CEF). Lymphocytes from B2B2 chickens bearing RSV-induced tumors lysed in vitro targets of B
2
B
2 and B
5
B
5 RSV-infected CEF and B
5
B
5 normal CEF, but did not lyse B
2
B
2 and B
24
B
24 normal CEF. Lymphocytes from normal B
2
B
2 chickens did not lyse any of the five types of CEF targets. Alloantisera absorption studies showed that both RSV-infected and uninfected CEF shared alloantigens, in particular B-F alloantigens, with syngeneic erythrocytes. Absorption with B
2
B
2 RSV-infected CEF significantly lowered the titer of B
2
B
2 anti-B
5
B
5 alloantisera. Cross-reactivity between B
5 antigen(s) and tumor-associated antigen was suggested and the nature of the cross-reactivity was discussed. It is hypothesized that this cross-reactivity prevents B
5
B
5 chickens from recognizing RSV-induced tumors as foreign, enhances tumor growth and leads to death of the host. 相似文献
106.
Cysteine metabolism has been thought to be important to the phenomenon of dimorphism inHistoplasma capsulatum. We sought mutants with genetic blocks in the metabolism of cysteine by selection of colonies resistant to the toxic analogue, selenocystine. The 22 resistant strains thus obtained were all deficient in uptake of cystine from the surrounding medium but were normally able to convert from mycelium to yeast and back again. Furthermore, they had normal quantities of NADH-dependent cystine reductase when this enzyme was measured. We conclude that mutants defective in cystine uptake can be readily obtained by selection of colonies resistant to selenocystine, and that a lesion in cystine-uptake does not appear to affect the phenomenon of dimorphism in this organism.Preliminary reports of this work were presented at the Second International Congress of Mycology, Tampa, 1977 and at the first International Conference on Histoplasmosis, Atlanta, 1978. 相似文献
107.
Eric Mundall 《Journal of insect physiology》1978,24(4):321-323
Yolk deposition begins in the terminal oocytes of virgins of Triatoma protracta a few days after adult eclosion, and while a few eggs may be matured before vitellogenesis ceases, none are laid. Mating at day four stimulates egg maturation and oviposition in fed and unfed females, egg-laying beginning as early as nine days after eclosion. If mating is delayed until day 16, by which time vitellogenesis normally has ceased, stored eggs are laid within two to four days and yolk deposition is resumed. Removal of the brain prevents oviposition, as does the severance of the ventral nerve cord. Thus, an intact central nervous system is required for egg-laying. Also, since neither operation inhibits egg maturation or ovulation, it appears that the latter reproductive responses to mating are independent of oviposition. 相似文献
108.
Eric R. Dabbs 《Molecular & general genetics : MGG》1978,165(1):73-78
Summary A strain of Escherichia coli, VT, which spontaneously gives rise to mutations in many ribosomal proteins, has been used in conjunction with chemical mutagenesis and varying the subsequent incubation temperature to select mutants which have alterations in every ribosomal protein amenable to analysis of 70 S proteins on two-dimensional polyacrylamide gels under standard conditions. Alterations have been detected in 50 ribosomal proteins, namely in 20 from the small and in 30 from the large subunit. This is the most complete set of mutants with altered ribosomal proteins described so far. The difficulty until recently in obtaining mutations in most ribosomal proteins arises not because they are lethal, as has often been supposed, but because of the lack of a suitable selection heretofore.Communicated by E. Bautz 相似文献
109.
110.