Estimation of helical angles of myosin and collagen by second harmonic generation imaging microscopy

We performed Second Harmonic Generation (SHG) imaging microscopy of endogeneous myosin-rich and collagen-rich tissues in amphibian and mammals. We determined the relative components of the macroscopic susceptibility tensor chi((2)) from polarization dependence of SHG intensity. The effective orientation angle theta(e) of the harmonophores has been determined for each protein. For myosin we found theta(e) approximately 62 degrees and this value was unchanged during myofibrillogenesis. It was also independent of the animal species (xenopus, dog and human). For collagen we found theta(e) approximately 49 degrees for both type I- and type III- rich tissues. From these results we localized the source of SHG along the single helix of both myosin and collagen.