Comparative Biochemistry and Physiology Part B: Comparative Biochemistry最新文献

We have studied the time course of hepatic and renal microsomal glucose-6 phosphatase (Glc-6Pase) during long-term fasting in the rat. Liver microsomal Glc-6Pase increases up to 48 hr and significantly decreases after 48 hr of fasting. The following activities were determined at 0, 24, 48, 72 and 96 hr: 0.31 ± 0.02; 0.50 ± 0.02; 0.54 ± 0.03; 0.44 ± 0.03; 0.44 ± 0.01 μmol min⁻¹ mg protein⁻¹, respectively (all values are means ± SEM, n = 6). Concomitantly, kidney microsomal Glc-6Pase progressively increases throughout the fast (V_m = 0.21 ± 0.01; 0.26 ± 0.004; 0.30 ± 0.01; 0.37 ± 0.02; 0.40 ± 0.01 μmolmin⁻¹ mg protein⁻¹, from 0 to 96 hr, respectively). These data suggest that the differential expression of Glc-6Pase activity in the liver and the kidney during long-term fasting could have an important role in the shift from a principally hepatic gluconeogenesis to a hepatic and renal gluconeogenesis.

The lack of hemoglobin and of carbonic anhydrase in the blood of icefish suggest that substantial adaptations of the acid-base balance should occur in order to ensure blood pH homeostasis. The level of peptidic histidyl and of reactive -SH groups per unit of body mass in icefish plasma are 12–13 times higher than those of Notothenia rossii, a common red-blooded Antarctic species. It is proposed that the high level of imidazole ring in icefish plasma improves the non-bicarbonate buffering capacity and that the reactive sulfhydryls are involved in a redox buffer as in some other hypoxia tolerant species. After plasma fractionation on Ultrogel AcA 34, the two main icefish serum proteins have been purified by DEAE cellulose chromatography (IFI) and by HPLC on anion exchange column (IF2). IFI has been identified as a cysteine-rich para-albumin and IF2 as an histidine-rich immunoglobulin-like protein.

The distribution of cyclic betaines were examined comparatively in several organs of 10 species of fish. The distribution of homarine depended on the organs and fish: high levels in gonads, and medium levels in digestive contents and digestive organs were found in Clupeidae and Engraulidae. Homarine was also present in undetected or small amounts in the remaining five species belonging to Plecoglossidae, Scomberesocidae, Carangidae, Sciaenidae and Monacanthidae. Trigonelline and N-methyl isonicotinic acid—isomers of homarine—were scarcely found. Homarine content in fish was not closely related to their food.

A recombinant phage clone containing a 1584 nucleotides rhodopsin cDNA was screened from a carp retinal cDNA library. The inserted DNA consisting of a single open reading frame of 1062 nucleotides at positions 72 to 1133 encodes a 354 amino acid polypeptide. The deduced amino acid sequence of carp rhodopsin showed 95.7, 85.5 and 74.4% identity with that of goldfish, sand goby and lamprey, respectively. The sites of palmitoylation, glycosylation, disulfide bond formation and Schiff base formation in the putative rhodopsin are all conserved.

The complete primary structures of two variants of a protein, Abd-5, isolated from the endocuticles of the migratory locust Locusta migratoria and the desert locust Schistocerca gregaria, have been determined. The proteins from the two species are N-terminally blocked with pyroglutamic acid. Their sequences differed only in two positions. Comparison of the sequences to those of other cuticular proteins shows that moderate homologies exist to 11 other cuticular proteins from insects representing four different orders. Amino acid residues in certain positions appear to be strictly conserved.

The optimum pH of the amylase was 6.5 at 30, 37, 40 and 50°C. At pH 6.5, the amylase had an optimum temperature of 25°C and activation energy (E_a) of 7.3 kcal/mol. The thermostability of the enzyme was determined at 45 and 50°C. The K_m values were determined at various temperatures and found to be lowest at 10 and 50°C and highest at 20°C.

An endoprotease in earthworm (Lumbricus rubellus) is purified to apparent homogeneity using ¹²⁵I-lactalbumin as a substrate. The protease has a molecular mass of 27 kDa and is markedly activated by poly-l-lysine or poly-l-arginine. It is a chymotrypsin-like serine protease. Its activity is distributed to coelomic fluid but relatively little to coelomocytes.

The gastrovascular fluids of the sea anemone Phymactis clematis display strong hemolytic activity, which has basic pH optimum, is thermolabile and is sensitive to proteases. The hemolytic agent from the gastrovascular fluid was partially purified by ammonium sulfate precipitation, chromatography on Dowex-50W cation exchanger and gel filtration on Sephadex G-50. A single peak elutes from the latter with an estimated mol. wt of 18,000. This elution pattern is unaffected if the chromatography is carried out in the presence of 5 M urea. These results indicate that the hemolytic activity is due to a single peptide or a group of peptides of similar size, which we here designate as “coelenterolysin”. Coelenterolysin is also present in sea anemone tissue homogenates, is different from the nematocyst toxin and is not associated with phospholipase activities. It is inhibited by sphingomyelin. This is the first report of hemolytic polypeptides associated with the coelenteric fluid of sea anemones. Coelenterolysin may have a role in extracellular digestion, defense against predators and invasion of the coelenteron by foreign organisms.

Wheat germ agglutinin (WGA) and Bowman-Birk soybean trypsin inhibitor represent potential transgene products for inducing pest resistance in plants. The effects of these molecules were studied on midgut esterase and protease activities from Apis mellifera L., a major insect pollinator. Trypsin inhibitor and WGA did not exhibit an acute toxicity in A. mellifera. In vivo, trypsin inhibitor caused a decrease in the amount of trypsin activity and did not have a significant effect on esterase activity. In vitro, trypsin inhibitor inhibited about 80% of non-specific protease activity and 100% of trypsin activity. In vivo, WGA at high concentration in food (1 mg/ml) elicited a large decrease in trypsin activity and did not have a significant effect on esterase activity. In vitro, WGA did not have any significant effect on trypsin and non-specific protease activities but slightly activated esterase activity.