Scientia Sinica最新文献

Establishing a model for various kinds of vivid metabolic systems of living organisms is an subject, uneasy but of great significance. Hill has constructed a theoretical framework for discussions of metabolic systems, such as active transport, muscle contraction, etc. The basic method of his framework is diagram calculation for the cycle flux on the metabolic cycles of those systems [2, 7] He has successively found that the result from diagram calculations agrees with the data of the numbers of completing different cycles given by random test (Monte Carlo test), but has not yet proved that the former is just the circulation rate in the sense of trajectory. In this paper, the model of a Markov chain is used to define the circulation rate in the sense of trajectories and, by deriving the remaining Markov chains, we calculate the expression of circulation rate which coincides with Hill's result obtained from diagrams. And hence we verify that Hill's cycle flux is equivalent to the circulation rate defined by trajectory. Besides, this paper establishes a connection between Hill's free energy of small systems and the potential of a Markov chain which is suggested by Hou Zhenting.

The mechanics of blood flow from a continuum point of view is considered. The basic laws of motion are reviewed and a set of constitutive equations appropriate for blood flow are derived. The thermodynamics of blood is studied and some restrictions on the coefficients of viscosity are derived. The theory allows for local variation of hematocrit in the flow and also indicates the possibility of supporting shear stress in zero shear rate. A simple free energy function is postulated and the basic equations of motion are derived and some special cases are discussed.

The theory of dissipative structure is applied to the study of atherosclerosis. An autocatalytic theoretical model is suggested. The behaviors of the model are in agreement with the facts of experimental atherosclerosis. We predict the high effectiveness of combinative therapy for atherosclerosis with drugs affecting protein metabolism and lipid metabolism. It was verified by animal experimentation. Further possible developments are briefly discussed. This work is the theoretical foundation of the Multi-Risk Factor Intervention trial (MRFIT) which is popularized clinically in its beginning all over the world.

The relationship between conformation change and activity of E. coli L-asparaginase has been studied with circular dichroism spectra and microcaloric methods. In many papers, it has been pointed out that the active site of L-asparaginase is closely related to tyrosyl residues. The present authors have studied the effects of L-cysteine on the activity and the conformation of L-asparaginase with UV difference spectra and kinetic methods. Moreover, we have studied the space arrangement of tyrosyl residues in the enzyme molecule. The results show that every enzyme molecule contains about 56 tyrosyl residues, 20 of which are in the hydrophobic core of the enzyme molecule, another 20 at the surface of the enzyme molecule, and the rest in the rifts and hollows of the enzyme molecule. Meanwhile, further study has also been made to determine the relationship between the changes of the enzyme activity and the ionization of tyrosyl residues as well as their chemical modification. By Zou Chenglu's graphical method we have proved that two tyrosyl residues at the surface of the enzyme molecule are the essential groups.

Comparative studies of the properties of murine haemopoietic stem cells from different sources revealed that the peripheral haemopoietic stem cell is relatively weaker than the haemopoietic stem cell from bone marrow in promoting the recovery of hemopoiesis in the irradiated animals. This is due to the heterogenity of stem cell population in which some aged cellsubpopulations are co-existing. The modified potential in proliferation and differentiation of haemopoietic stem cells in the peripheral blood seems to be irreversible under normal physiological conditions. In a preliminary experiment, the use of an anti-thymocyte immunoglobulin to eliminate immunocompetent cells proved effective in reducing the severity and incidence of secondary diseases and in increasing the number of survivors of lethally irradiated semi-isologous mice after transplantation of parental peripheral mononuclear cells.

Visual responses of 125 units have been extracellularly recorded with glass micropipettes from the left nucleus isthmi in the frog Rana nigromaculata, and 101 electrode tip positions marked with cobalt staining to reconstruct a visual field map in the nucleus. 80% of the units recorded show ON-OFF responses to a stationary spot of light and many are directionally selective in response to black or white targets moving through their receptive fields. All the cobalt-marked spots are within the nucleus, indicating that the nucleus isthmus proper is a restricted part of the frog visual system. There is a visual field map in the nucleus. The entire contralateral hemifield and the nasal 40 degrees of the ipsilateral hemifield project on the nucleus topographically. A cell-free band inside the nucleus is a boundary line separating the contralateral hemifield from the ipsilateral one. Dorsal to it is the contralateral field representation. The upper visual field projects on the rostral half of the nucleus and the central and medio-ventral portion of its caudal half. The lower field is represented on the dorsal and lateral part of the caudal half. Fifteen binocular units have been found from the nucleus, 13 of which are dominantly activated by the contralateral eye, the other two are almost equally excited by either eye. These binocular units are mainly situated in the medulla of the rostral half of the nucleus isthmus.