The authors have isolated and partial purified antifreeze protein antifreeze protein (AFP) produced endogenously in Ammopiptanthus mongolicus.The results show that the partial purified AFP ranged in size including 45 7 kD, 81 2 kD, and so on.At 50 mg/ml protein concentration, the temperature of melting point is -15℃, and its freezing point is even lower.Therefore, the AFP activity exhibited by the Ammopiptanthus mongolicus is higher than that observed for AFP found in polar fishes or in winter rye.In addition, by a phase contrast light photomicroscope, the author have observed the morphology of individual ice crystals formed in the solution, including squares, rectangles, cones, hexagons.The morphology of these ice crystals are similar to those of ice crystals observed in polar fishes and in cold acclimation winter rye.
The genomic library of a cold-resistant fresh water teleost, Leuciscus waleckii,was constructed by using phage EMBL3 as vector. Three positive liybridized recombinant phage plaques were screened out by AFP gene probe of a marine teleost, North American winter flounder(Pseudopleur-onectes americanus).Three positive hybridized bands of 2.7 Kb/Sac I, 8 Kb/BamHI and 20 Kb/Hind III DNA segments obtained from these positive hybridization recombinant phage DNA were identified when a AFP gene and a 0.4 Kb cDNA of AFP gene of a marine teleost,the winter flounder, were used respectively as the probes for Southern analysis.These preliminary results show that a homologous sequence of AFP gene of winter flounder seems to be present in the genome of Leuciscus waleckii.
The conventional protein chromatography technique was adopted to purify the antifreeze proteins (AFPs) from the leaves of Ammopiptanthus mongolicus (Maxim.) Cheng f. Two bands on native PAGE gel showed thermal hysteresis activity, one was band B1, whose thermal hysteresis was 0.46 ℃ at 8 g/L, which showed two bands (67 kD, 21 kD) on SDS_PAGE gel; the other was B3, whose thermal hysteresis was 0.45 ℃ at 10 g/L, and it contained only a single protein (39.8 kD). Both B1 and B3 are not glycoproteins, because neither do they interact with Shiff_reagent, nor show ultraviolet characteristics of a typical glycoprotein.
