A METHOD FOR DETERMINING THE RENNET ACTIVITY OF CHYMO-TRYPSIN

The rennet activity of chymo-trypsin (or pepsin) is conveniently measured by allowing a standard solution of milk to which chymotrypsin has been added to flow slowly through a graduated pipette and observing the rate and distance of flow of the milk before it clots. The time required for chymo-trypsin to clot milk may be calculated from these observations. The rennet activity is expressed as the reciprocal of the time in minutes required for 1 ml. of enzyme solution to clot 10 ml. of standard milk powder solution.     

A METHOD FOR THE QUANTITATIVE DETERMINATION OF TRYPSIN AND PEPSIN

A quantitative method is described which permits a determination of the relative amount of trypsin or pepsin present in a gelatin-enzyme digestion mixture, provided the gelatin and trypsin solutions are purified. This method is dependent upon the change in viscosity of such solutions. It is found that the time required to cause a given percentage change in the viscosity is nearly inversely proportional to the amount of enzyme present. It is pointed out that the particular value of the method lies in the fact that enzyme reactions which take place in the presence of "buffer" salts may be studied.     

METHODS FOR DETERMINING THE PROLIFERATION KINETICS OF CELLS BY MEANS OF 5-BROMODEOXYURIDINE

After treatment of cells with 5-bromodeoxyuridine (BUdR), the percentage of completely BUdR-labelled interphase nuclei is greater the longer the BUdR treatment. The labelling effect is visible after staining with the fluorochrome 33258 Hoechst and with Giemsa. Various formulae and a nomogram are presented by means of which the percentage of cells in S period, duration of the S period and the whole cell cycle can be determined by examination of a single preparation or by comparison of several preparations. The methods are tested using cell cultures of Microtus agrestis and compared with autoradiographic methods after labelling with ³H-thymidine.     

IMMUNOLOGICAL STUDIES ON PEPSIN AND PEPSINOGEN

1. Alkali (pH 7.6)-denatured pepsins from swine, cattle, and guinea pigs precipitate in swine pepsin antiserum. Similarly treated pepsins from the rabbit, chicken, and shark do not. 2. Pepsin antisera react with both pepsin and pepsinogen, but do not react with the serum proteins from the homologous species. 3. Pepsinogen antisera react with pepsinogen, but not with twice crystallized pepsin, nor with the serum proteins from the homologous species. Positive reactions between activated pepsinogen and pepsinogen antiserum have been observed. It was possible to remove the reacting material from either the pepsinogen or the activated pepsinogen mixture. 4. Antisera made with serum proteins do not react with the homologous pepsin or pepsinogen.     

植物基因克隆的策略和方法

本文介绍了功能克隆,定位克隆,表型克隆等９种克隆植物基因的方法,着重分析了每项克隆方法的工作原理,应用范围和进展     

NONPARAMETRIC MODELS FOR DISCRIMINATION METHODS AND SENSITIVITY ANALYSIS FOR TRIADS

Nonparametric models for sensory discrimination methods are developed. In these models, the relationship between the probability of a correct response, P_c, and the measures for sensory discriminability or sensory difference, p₁ and p₂ are given. On the basis of the models, different sensitivities for triadic tests were compared including 3-AFC and triangle methods with the strong stimulus as the odd sample and with the weak stimulus as the odd sample. Predictions were made which can be tested experimentally.