Comparative Biochemistry and Physiology Part A: Physiology最新文献

We investigated the abilities of sparrows, Zonotrichia leucophrys, to adjust their rates of oxidation of endogenously derived essential amino acids and to retain these indicator amino acids (IAA) in tissue proteins in response to either a dietary deficiency of total protein, threonine or sulfur amino acids (SAA). Tissue proteins of birds were uniformly labeled with either 1-¹⁴C-phe or 1-¹⁴C-val by injecting birds IM with a tracer dose of labeled amino acid 21 days before dietary treatments began. Oxidation rates and retention of IAA in tissue proteins were compared between well-nourished birds and those fed deficient diets during two phases of their annual cycle, molt and winter maintenance. Non-molting birds fed diets low in protein or in threonine and molting birds fed diets low in protein reduced oxidation rates and increased retention of IAA after 9 days of dietary treatment as compared with well-nourished birds. In contrast, non-molting birds fed diets low in SAA showed no adjustments in oxidation or retention of IAA and molting birds fed diets low in SAA showed increased rates of oxidation and lower retention of IAA as compared with well-nourished control birds. In those birds able to adjust to dietary deficiencies, decreased oxidation and increased retention rates closely approximated earlier reported decreases in muscle protein degradation rates in response to malnutrition. Reduced protein degradation rates may be the preeminent compensatory mechanism in protein sparing during malnutrition, whereas adjustment in oxidation and reutilization of endogenously derived amino acids seems to play only a small role. Differing responses of birds to SAA deficiency as compared with protein or threonine deficiency probably result from depletion of glutathione pools and a resulting disturbance to the normal economy of protein metabolism.

Ten hemoglobins from the teleost Micropogon undulatus were separated in native polyacrylamide gel electrophoresis. In a large sample taken from a tributary of the Chesapeake Bay in Virginia, the distribution of these hemoglobins confirmed a polymorphic condition, which was previously known in North Carolina animals. The intraspecific variation was unrelated to body length, indicating that it is an adult phenomenon. The 10 hemoglobins were expressed in seven different phenotypic banding patterns. Although several morphs were infrequent, no single phenotype comprised a majority of the sample, indicating that the variation is quite great. Several phenotypes differed from those in North Carolina animals and, conversely, several North Carolina phenotypes were not recovered from the Chesapeake Bay sample. This finding suggests that the polymorphism is more complex than observed in either investigation alone. The O₂ binding of hemolysates stripped of co-factors by dialysis revealed functional differences between some, but not all, Chesapeake Bay morphs. The most variable property was O₂ affinity, although a few differences in pH dependence and cooperativity were also observed. The O₂ binding of red blood cell preparations also differed. These differences were not identical to those between dialyzed hemolysates, suggesting that organic PO₄ co-factors may be involved as well.

As part of our ongoing research on cardiac hypoxia tolerance we have conducted ³¹P nuclear magnetic resonance (NMR) studies of isolated, perfused, working hearts from freshwater turtles, animals that are well known for their ability to tolerate prolonged periods of anoxia. A striking feature of turtle heart spectra is an extremely high concentration of NMR visible phosphodiesters (PDEs). Cardiac spectra from mammals, on the other hand, typically exhibit only a small resonance in the PDE region. Our aim in this study was to compare myocardial PDE profiles between the highly hypoxia tolerant western painted turtle (Chrysemys picta bellii) and the relatively hypoxia sensitive softshelled turtle (Trionyx spinifer) in order to begin to test the hypothesis that high constitutive levels of cytosolic PDEs may play a role in conferring hypoxia and ischemia tolerance on the myocardium. We also collected ³¹P-NMR spectra of PCA extracts of tissue from these species and from Kemp's ridley sea turtles (Lepidochelys kempi), as well as spectra from isolated hearts and PCA extracts of redeared sliders (Trachemys [formerly Pseudemys] scripta]). Total NMR visible phosphodiesters make up 24 ± 8.6% of the total NMR visible phosphorus in chrysemys hearts, 20.7 ± 5.9% in Trachemys hearts, but only 12.2 ± 5.1% in Trionyx hearts (P < 0.05). We have identified three distinct PDEs in turtle hearts: glycerophosphorylcholine (GPC); glycerophosphorylethanolamine (GPE); and serine ethanolamine phosphodiester (SEP). SEP is the dominant compound in Chrysemys and Trachemys (79.3 ± 10.2% and 84.7 ± 3.7% of total PDE, respectively), while GPC is most abundant in Trionyx (74.0 ± 4.3% of total PDE) and Lepidochelys (not quantitated). The function of this class of compounds is unclear but it has been suggested that cytosolic PDEs may function as lysophospholipase inhibitors, a role that would decrease the rate of membrane phospholipid turnover. Our comparative data suggest that cytosolic PDEs could play a role in phospholipid sparing during anoxic or ischemic stress in turtles but a direct test of this hypothesis awaits future experimentation.

Hemagglutinins were determined in six species of mosquitoes that are susceptible and refractory to Brugia malayi (Filarioidea: Nematoda). High titers of hemagglutinins were found in the salivary gland extract and in the body fluid of a completely refractory species, Aedes taeniorhynchus, and in partially refractory species, Anopheles quadrimculatus; but low levels of hemagglutinins were also present in the body fluid of Aedes aegypti (Black-eye, Liverpool strain), a susceptible species. Hemagglutinating activity was not found in the other three completely refractory species of mosquitoes, Culex quinquefasciatus, Culex nigripalpus, and Aedes albopictus in which blood coagulated rapidly after ingestion. High titers of hemagglutinins in the salivary glands of Ae. taeniorhynchus and An. quadrimaculatus facilitated rapid movement of sheathed microfilariae from the midgut to the hemocoel. It is suggested that high titers of hemagglutinins present in the hemocoel bound to the glycoconjugates with exposed carbohydrate moieties present on the microfilarial sheaths and developing abnormal larvae (L₁) in the thoracic muscle cells. These hemagglutinin-bound glycoconjugates formed capsules that subsequently stimulated the immune response and resulted in melanization of microfilarial sheaths and sheathed microfilariae in the hemocoel and intracellularly developing abnormal L₁ in the thoracic muscles. Only minimal encapsulation and melanization of B. malayi microfilariae was observed in the hemocoel of the other four species of mosquitoes that lacked hemagglutinins in the salivary glands. The results suggest that tissue specific hemagglutinins are one of several factors of vector susceptibility/refractoriness through immune reactions (encapsulation, activation of prophenoloxidases).

The sex- and developmental stage-specific occurrence of gelatin-degrading enzymes has as yet never been systematically investigated in any insect species. By way of zymographic analysis, gelatinolytic activity was analyzed in the hemolymph and homogenates of the gray fleshfly Neobellieria bullata. Gelatinolytic activity was detected in feeding larvae and disappeared from both hemolymph and total body extracts during the wandering stage. An increase in gelatinolytic activity is observed around the third day after pupariation and again in late pharate adults. In adult females, gelatinolytic activity is only present in the hemolymph during the vitellogenic stages, whereas it is undetectable in the adult male hemolymph. Gelatinolytic activity is high in the fat body of vitellogenic females but low in that of previtellogenic females and in males. Injection of 20-OH-ecdysone induces gelatinolytic activity in previtellogenic females and in liver-fed males. In vitro, this hormone triggers gelatinase production by the fat body of liver-fed males but surprisinly not by that of sugar-fed (previtellogenic) females, which indicates that ecdysteroids are not the only regulatory molecules involved. Our data suggest that in Neobellieria, and perhaps in other insects as well, gelatinolytic activity is indirectly involved in growth, metamorphosis and reproduction.

Blood acid-base homeostasis of the hemoglobinless Antarctic teleost Chionodraco hamatus was analyzed by measuring the titratable buffer capacity (β) and carbonic anhydrase (CA) activity in blood smaples. Results were compared with those obtained in the red-blooded temperate fish Anguilla anguilla. Data show that the titratable blood buffer capacity of icefish, in the range of red-blooded teleost species, was significantly higher than that of A. anguilla. Furthermore, plasma inorganic phosphate and reactive sulfhydryl content was significantly higher in the Antarctic species. No enzymatic activity of CA was detected in blood samples of Antarctic fish, suggesting the absence of a blood CA-isozyme.