Évolution moléculaire des hémoglobines et des cytochromes ; quelques conceptions actuelles sur l'écologie et l'évolution moléculaires humaines

Abstract

Summary The study of the molecular evolution of cytochromes and haemoglobins permits to set forth the following points : 1. — It is possible to improve the study of the haemoglobin and cytochrome conformational dynamics by analysing, in comparative biochemistry, stable polypeptidic sequences which do not admit mutation. These active zones are quite stable as far as cytochromes are concerned and have little varied in the course of evolution whereas the genie systems of a, (3, y an(^ S chains of haemoglobins are comparatively more tolerant. The most tolerant functional molecules being fibrinopeptides. 2. — The study of cytochromes and more particularly of the С cytochrome permits to reconstruct molecular evolution history, much before the existence of primates, before the moment when the animal kingdom and the vegetal one became distinct. Such methods are likely to give one day, as Dickerson says, precise dates for events as remote as the separation of plants and animals, the origin of nucleate cells or even remote separations in life history. 3. — As for molecules such as globins, less ancient than cytochromes, one can say that the genes giving present human haemoglobins are about 950 million years old. Comparative molecular analysis permits to follow the evolution of the different polypeptidic chains from most ancient globins the present myoglobin can give an image of : — the genes giving the α and β chains of the present haemoglobins are about 500 to 600 years old ; — the genes giving the γ chains are more recent. They are no more than 200 million years old ; — the individualization of δ chains probably from β chains come far later the primates got separate. 4. — The immunological and immunoelectrophoretical study permits today — as far as other genie systems are concerned — to complete the individualization of human genome history and to give precisions about how old such genie systems are, in reference to hominisation : — the genes of ABO and MN systems appeared before hominisation ; — the genes of rhesus systems, strongly polyallelic, are contemporary with hominisation ; — genie systems defined by electrophoresis (immunoglobins, Gm and Inv systems) were at their best at the moment when races appeared. Therefore they constitute racial marking genes. — The genes which determine the abnormal HbS and HbE haemoglobins are still more recent since they cover only fragments of races. 5. — The study of this genie evolution seen through the molecular one has permitted us to set forth what we call « ECOLOGICAL MAGNIFICATION » given by mutated genes — which is particularly evident for the different haemoglobin chains. The inner or outer ecological conditions select the most convenient « allosteric transition ». 6. — The duplication of one gene on the same chromosome which is particulary evident for the genie systems of the globins is able to give numerous genes with strong adaptative potentiality. The genes of α and β chains illustrate what has just been said. 7. — Such ecological magnification can be noticed throughout animal world including human species with the appearance of « ECOPROTEINS » (α2γ2 and α2δ2 chains). These proteins which are new or pre-existing ones are likely to represent a process of physiological molecular adaptation, « an ecological feed-back ». The originality of ecoproteins derives from their allosteric function which is particular. That is probably the case for the globinical a2d2 and aoyo chains of fœtus proteins strongly responding to the oxygen factor. Besides haemoglobins, ecoproteins may represent, in some cases, allosteric effectors whose connections with allosteric locations depend on the environment, that is to say are « ecodependent » (ecoproteins are ecodependent proteins). 8. — We insist upon the importance of different types of mutations (Robertson fusion, duplication of one gene on the same chromosome, genie magnification, genie Testification). These facts associated with ecological magnification which takes place particularly when the best allosteric molecular transitions are selected permit to get a closer view upon the apparent evolutive accelerations in the course of evolution and upon hominisation in particular — even if « mutation rates » remain constant.