Investigation of ribonuclease-catalysed kinetics by a micro-calorimetric method.

A rapid micro-calorimetric method for the simultaneous determination of the Michaelis-Menten parameters and the enthalpy of enzymic reactions is developed. The hydrolysis of 2': 3'-cyclic CMP by ribonuclease A is studied to test the proposed method; values obtained are in good agreement with already published data. Enzymic hydrolysis of yeast RNA, unlike that of cyclic phosphates, is shown to be endothermic. This result is explained by the two-step mechanism of this reaction

Iso-cytochrome c species from baker's yeast. Analysis of their circular-dichroism spectra.

The circular-dichroism spectra of baker's-yeast iso-1- (methylated and unmethylated forms) and iso-2-cytochrome c species were examined between 200 and 600nm. In the visible region the yeast haemoproteins have characteristics nearly indistinguishable from those of horse heart cytochrome c. From the spectra in the u.v. region the latter appears, however, to be more helical. It is proposed that the likely element of non-helical structure in iso-1-cytochrome c is residues 62-70