so 4 solution and precipitated into 5 317 ml proh containing 1 3 h 2 o the obtained suspension was centrifuged and washed once with 1 proh 1 3 h 2 o the fine particles were essentially of the same appearance as obtained with subtilisin see example 1 the following samples were measured on a jasco j 600 spectropolarimeter under pc control insulin co precipitated with k 2 so 4 as described above the spectra obtained were very similar both to each other and to a literature spectrum showing that insulin substantially retains its native structure following precipitation and redissolution dna genomic ultrapure from calf thymus with average molecular weight 8 6 mda corresponding to approximately 13 kbase pairs was bought from sigma 0 5 unit of dna was dissolved in 100 u03bcl and mixed with 300 u03bcl of a saturated k 2 so 4 solution this was added to 4 5 ml of 1 proh previously dried over molecular sieves resulting in immediate formation of a fine precipitate the suspension was shaken at 600 rpm for 2 mins allowed to settle and centrifuged in eppendorfs at 6000 rpm the proh supernatant was removed and the precipitate redissolved in 1 ml of 10 mm tris hcl buffer ph 7 8 containing 1 mm edta and 1 mm nacl the uv spectrum of the precipitate was compared with.