Vibrational circular dichroism of polypeptides. II. Solution amide II and deuteration results

Vibrational CD (VCD) of amide I and II vibrations of several α-helical polypeptides have been measured in solution. For the amide II as well as the amide I [previously published: Lal, B.B. & Nafie, L.A. (1982) Biopolymers 21 , 2161] we find the VCD to be characteristic of the polypeptide secondary structure. Amide II bands of right-handed α helices were all found to have negative VCD and to have their maximum rotational strength for the parallel (low-energy) component. However, left-handed α helices formed from L -amino acids gave positive amide II bands at higher frequencies than found for the right-handed helices, indicating that the VCD was sensitive to the stereochemical difference. The amide-I VCD spectra of some deuterated right-handed α-helical polypeptides have a new negative feature to low frequency that does not reflect theoretical predictions but also appears to be stereochemically sensitive. Amide-II and amide-A VCD of a few deuterated polypeptides imply retention of the secondary-structure-dependent characteristics seen in the hydrogenated VCD.     

Phototropism. II

The Botanical Review - The major revisions which we must make in our ideas concerning phototropism are the following:     

Plant Nucleases. II. Properties of Corn Ribonucleases I and II and Corn Nuclease I

Three enzymes with ribonuclease activity, one of which also had deoxyribonuclease activity, have been isolated and partially purified from corn seeds and seedlings. The purification of Ribonuclease I from mature seed was previously reported. This enzyme has a pH optimum near 5.0, is loosely adsorbed to carboxymethyl-cellulose, and has a molecular weight of 23,000, determined by gel filtration.

Ribonuclease II was isolated from the microsomes of corn roots, and was partially purified by gel filtration. It has a pH optimum plateau from 5.4 to 7.0, and molecular weight of 17,000.

Nuclease I hydrolyzes both RNA and DNA. It was isolated from the large particles of a corn root homogenate and was partially purified on a carboxymethyl-cellulose column. It has a pH optimum at 6.2 and a molecular weight of 31,000.

The relative activities of the 3 enzymes for deoxyribonuclease and at pH 5 and pH 6.2 for ribonuclease may be used to characterize them during purification operations. Assays on homogenates of corn roots, and especially of the root tips, suggested that a fourth enzyme, which possesses deoxyribonuclease activity, is also present.