Search PubMed⌕ Search

Biomedical subjects

H C Li

Publications and source records attributed to H C Li.

108 records · Page 6Linked to original sources
PubMed1976

Biochemical actions of fibroblast kinin-forming protease.

Purification and further characterization of a kinin-forming acid protease in a mouse fibroblast L929 stationary cell culture line was carried out. Supernatants of dialyzed fibroblast homogenates digested denatured hemoglobin at pH 4.0. The supernatant was fractionated on a G-200 Sephadex column, hydroxylapatite column and finally on a DEAE-A50 Sephadex ion exchange column. A 9.4 fold purification was achieved with a 13.8% yield. The enzyme had a specific activity of 2062 ng kinin per mg protein when measured on a purified rat kininogen using the isolated rat uterus as the bioassay tissue. The protease had a pH optimum of 3.8-4.0. Molecular weights of the enzyme and substrate estimated on a G-200 Sephadex column were 39,000 and 110,000 respectively. Kinin formation was a function of both incubation time and enzyme concentration. Protease activity was localized primarily in the 10,000 g supernatant cell fraction (61.5%) with the 1500 g precipitate cell fraction containing 38.5% of the activity.

Cell Line↗
PubMed1975

Phosphoprotein phosphatase-catalyzed dephosphorylation of the 22,000 dalton phosphoprotein of cardiac sarcoplasmic reticulum.

The present study demonstrated the presence within the myocardium of phosphoprotein phosphatase activity which can account for dephosphorylation of a 22,000 dalton phosphoprotein of cardiac sarcoplasmic reticulum that has been associated with the stimulatory effects of adenosine 3':5'-monophosphate (cyclic AMP)-dependent protein kinase on calcium transport (Tada, M., Kirchberger, M. A., and Katz, A. M. (1975) J. Biol. Chem. 250:2640-2647). Dog cardiac microsomes, consisting mainly of fragmented sarcomplasmic reticulum, were phosphorylated by incubation with cyclic AMP-dependent protein kinase and [gamma-32P]ATP, and subsequently washed with trichloroacetic acid or buffered KCl. Phosphorylated microsomes contained approximately 1 nmole of 32P bound per mg of microsomal protein, 32P labeling occurring almost exclusively at the 22,000 dalton component. Soluble phosphoprotein phosphatases, isolated from the cytosol, catalyzed dephosphorylation of 32P-labeled microsomes. The existence of a phosphoprotein phosphatase that is associated with the microsomes was demonstrated by the ability of the microsomes to dephosphorylate 32P-histone. This membrane-associated phosphatase activity can also account for a rapid decrease in the amount of 32P-labeling of the 22,000 dalton protein. The dephosphorylation of the phosphorylated 22,000 dalton protein by phosphoprotein phosphatase satisfies an important requirement for the phosphorylation of the 22,000 dalton protein to serve a physiological role, namely, its reversibility.

Animals↗
PubMedDate not supplied

The mobility of troponin C and troponin I in muscle.

In vertebrate skeletal muscle, contraction is initiated by the elevation of the intracellular Ca2+ concentration. The binding of Ca2+ to TnC induces a series of conformational changes which ultimately release the inhibition of the actomyosin ATPase activity by Tnl. In this study we have characterized the dynamic behavior of TnC and Tnl in solution, as well as in reconstituted fibers, using EPR and ST-EPR spectroscopy. Cys98 of TnC and Cys133 of Tnl were specifically labeled with malemide spin label (MSL) and indane dione nitroxide spin label (InVSL). In solution, the labeled TnC and Tnl exhibited fast nanosecond motion. MSL-TnC is sensitive to cation binding to the high affinity sites (tau r increases from 1.5 to 3.7 ns), InVSL-TnC s sensitive to the replacement of Mg2+ by Ca2+ at these sites (tau r increase from 1.7 to 6 ns). Upon reconstitution into fibers, the nanosecond mobility is reduced by interactions with other proteins. TnC and Tnl both exhibited microsecond anisotropic motion in fibers similar to that of the actin monomers within the filament. The microsecond motion of TnC was found to be modulated by the binding of Ca2+ and by cross-bridge attachment, but this was not the case for the global mobility of Tnl.

Animals↗