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.
Differential scanning calorimetry（ DSC） was used to measure the thermal hysteresis activity(THA) of plant antifreeze proteins(AFPs). The results reveal that DSC is a good method to screen and study AFPs. In the sixteen components extracted from Ammopipanthus mongolicus leaves, one(P3S1) was found to have apparent thermal hysteresis activity by DSC. As the amount of ice nuclei in the sample decreased, the THA of P3S1 increased from 0.01℃ to 0.65℃ . It is notable that the two- peak thermal hysteresis effect was observed. Two endothermic peaks appeared in the melting process of P3S1, while the freezing peak also consisted of two peaks. The peaks appeared antecedently showed larger thermal effect. This phenomenon shows P3S1 has two different kinds of interaction with water and ice crystal. It is probably an important property of a class of AFPs.
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.
