Abstract. The following question has recently arisen in the literature concerning the interpretation of the optical activity of biological membranes: do the characteristic spectral distortions observed for diverse membrane systems reflect some common and unique aspect of membrane architecture or are they the result of scattering effects owing to the particulate nature of membranous systems? We have confirmed the latter interpretation on the basis of the following experimental observations: (a) red blood cell membranes give a normal circular dichroism spectrum when scattering is reduced and (b) nonaggregated, nonmembranous helical proteins give distorted membranelike spectra when scattering is introduced. An improved estimate of secondary structure on the basis of undistorted spectra results in about 50 per cent a-helix for red blood cell membrane protein. In addition we conclude that the distortions in optical activity spectra offer no evidence in support of various proposed membrane models.During recent years there has arisen a literature concerning the optical rotatory dispersion and circular dichroism of biological membranes.1-9 Optical activity is a sensitive measure of the secondary structure of proteins and offers an attractive nondestructive probe of intact membrane structure. Many different membrane systems have given very similar optical rotatory dispersion and circular dichroism spectra, resembling an a-helical protein, but with characteristic distortions in relative intensity of the 208 nm 7r-r* to 222 nm n-7r* troughs, and red shifts in the n-7r* trough and crossover wavelengths. Several interpretations have been offered to account for these distortions in the membrane spectra. It was first proposed that since this unique spectra occurs in diverse membrane systems, it must represent some common aspect of membrane architecture, e.g., protein aggregation with possible alignment of a-helicesl 2 or hydrophobic interaction between protein helices and lipid.3 On the other hand, there has been the recent proposal of Urry and Ji8'9 that the distortions in the membrane spectra are the result of scattering artifacts owing to the particulate nature of the system. There is some evidence correlating turbidity with spectral distortions,2'9 but most of these experiments do not distinguish between effects resulting from scattering and those resulting from aggregation-induced polypeptide interactions. Ji and Urry's9 results on sonicated mitochondrial membrane fractions are the most convincing. However, since mitochondrial membranes are notably heterogeneous and a spectrum of the total sonicate was not 793

Proteinase activities in human seminal plasma were detected using gelatin-containing sodium dodecyl sulphate-polyacrylamide gel electrophoresis zymography. Three prominent bands of activity of Mr 60,000, 66,000 and 90,000 were observed as well as 9 other bands of less intensity (34,000-158,000). These proteinases were dependent upon calcium for optimal activity, did not hydrolyse casein, and were predominantly in the soluble portion of seminal plasma. Examination of seminal plasma of men with different sperm concentrations, split ejaculates, and prostatic secretions indicated that the prostate gland was a source of most of these activities. Proteinase activities of Mr 34,000, 37,000, 82,000 and 120,000 were expressed more frequently in seminal plasma from normozoospermic men than from seminal plasma of oligo- or azoospermic men, indicating that they may also arise from spermatozoa in the semen sample. The proteinases of Mr 60,000 and 66,000 were found in all seminal plasmas whereas there was variation in the expression of the other molecular forms of enzyme, even in the normozoospermic samples. There are multiple forms of gelatinolytic proteinase activities in human seminal plasma which appear to arise from multiple sources in the reproductive tract including the Cowper's/urethral glands, the prostate gland, seminal vesicle and/or spermatozoa. Their function(s) in semen remains to be established.