. Aspects of the origin of life. Life; Biochemistry; Biochemistry; Biogenesis. Protein Complexes as Biochemically Active Systems 185 As pointed out above, there are a number of indications that the activity of certain enzymes is altered in the presence of nucleic acids. The study of these phenomena has in the main centred around the role of ribonucleic acid and has been carried out, for the most part, at pH values below the isoelectric point of the enzyme and the substrate. In these conditions, as is known, insoluble nucleo- proteins are precipitated, this being the result of the formation of
. Aspects of the origin of life. Life; Biochemistry; Biochemistry; Biogenesis. Protein Complexes as Biochemically Active Systems 185 As pointed out above, there are a number of indications that the activity of certain enzymes is altered in the presence of nucleic acids. The study of these phenomena has in the main centred around the role of ribonucleic acid and has been carried out, for the most part, at pH values below the isoelectric point of the enzyme and the substrate. In these conditions, as is known, insoluble nucleo- proteins are precipitated, this being the result of the formation of salt-hke hnks between the acid and basic groups of the reactants. We thought that it might be preferable to study the effect of deoxyribonucleic acid (DNA) on the proteolytic process under conditions in which the interaction of DNA with the enzyme does not cause precipitation. Therefore we conducted our experiments at pH values above the isoelectric point of trypsin and serum albumin, , at the optimum values for proteolysis (phosphate buffer, pH 8-8-4). The DNA used was obtained. Fig. 5. The kinetic curves for the proteolysis of serum albumin by trypsin (I) and by trypsin with DNA (II). from calf's thymus. The molecular weight of the DNA, determined viscosi- metrically [29] was o-8-i-5-io6. The kinetics of proteolysis were determined by the modified spearophotometric method of Kunitz at 400 mix. Fig. 5 gives the kinetic curves for the proteolysis of serum albumin by trypsin (curve I) and trypsin with DNA (curve II). Here the difference between the initial and subsequently measured value of extinction (the latter in percentages of the initial value) is plotted against the time in hours. It is apparent that in the presence of DNA the proteolytic process is retarded and the degree of hydrolysis decreased. To gain an insight into the mode of inhibition of proteolysis by DNA we studied the effect of preliminary incubation of the enzyme or substrate with DNA. The curves obtained
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