Interactions of troponin I and its inhibitory fragment (residues 104-115) with troponin C and calmodulin

Fluorescent probes have been used to study the interaction of troponin I and its inhibitory peptide TnIp with troponin C, calmodulin, and the proteolytic fragments of calmodulin. The probes used included the noncovalently bound ligand TNS and the covalently attached labels dansyl and AEDANS. The fluorescence intensity of TNS bound to troponin C, calmodulin, or the calmodulin fragments was greatly enhanced by the presence of TnIp. This effect was used to estimate the corresponding binding constants. It was found that TnIp is bound by the C-terminal half-molecule of calmodulin, TR2C, with an affinity comparable to that of intact calmodulin or troponin C, while the binding affinity of the N-terminal half-molecule, TR1C, was an order of magnitude less, suggesting that the TnIp-containing portion of troponin I combines with the C-terminal half of calmodulin or troponin C. The fluorescence properties of an AEDANS group linked to Cys-98 of troponin C were modified by interaction with troponin I or TnIp. The fluorescence properties of the same group linked to Cys-27 of wheat germ calmodulin were affected by TnI, but not TnIp. TnI had a small effect upon the fluorescence of a dansyl group linked to Met-25 of troponin C. TnIp also inhibited the tryptic hydrolysis of the midpoint of the central connecting strand of calmodulin and troponin C.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma reproductive hormones in normal and vasectomized Chinese males

Plasma reproductive hormones (testosterone, LH, FSH and prolactin) were measured in 298 normal healthy males aged 30-73 years from rural areas of Sichuan Province, People's Republic of China, and in 505 similar men vasectomized between 1 year and 25 years previously. Age-related increases in LH and FSH but not in testosterone or prolactin were noted in normal men. No adverse effects of vasectomy were observed apart from a 16% increase in mean LH levels in the vasectomized compared to non-vasectomized men of similar ages.