Ribonuclease volume changes

In a measurement of a hydrophobic activation volume, Kettman et al. (1966) found a large positive volume change when ribonuclease molecules with attached polyvalyl chains were made to aggregate under pressure. Work is also in progress on the interaction kinetics... 

The few investigations reported on proteins under pressure (cf, e.g., the values for ribonuclease. Table 11) showed that the volume effects were insignificant or rather small, at least for pressures below 50 MPa. Recently, volume changes associated with temperature and pressure unfolding has been observed in the case of staphylococcal nuclease [2001S1]. 

The secondary and tertiary structures of myoglobin and ribonuclease A illustrate the importance of packing in tertiary structures. Secondary structures pack closely to one another and also intercalate with (insert between) extended polypeptide chains. If the sum of the van der Waals volumes of a protein s constituent amino acids is divided by the volume occupied by the protein, packing densities of 0.72 to 0.77 are typically obtained. This means that, even with close packing, approximately 25% of the total volume of a protein is not occupied by protein atoms. Nearly all of this space is in the form of very small cavities. Cavities the size of water molecules or larger do occasionally occur, but they make up only a small fraction of the total protein volume. It is likely that such cavities provide flexibility for proteins and facilitate conformation changes and a wide range of protein dynamics (discussed later). 

Ribonuclease Hydrolysis of pyrophosphate bonds in ribonucleic acids Antiviral Spectrophotometry One unit produces soluble oligonucleotides equivalent to a change in absorbance at 260 nm of 1.0 in 30 min at pH 7.5 and 37°C in a 1.5 ml reaction volume... 

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