Horse and cow cytochrome c differ in amino acid sequence by three residues. Candida krusei cytochrome c contains 5 more residues than horse cytochrome c and differs in sequence at 45 of the 103 residues common to both proteins. The denaturation by guanidine hydrochloride (Gdn HCI) and acid has been studied to determine the effect of the differences in sequence on the relative stabilities of these homologous proteins. Denaturation was followed using optical rotation measurements at 300 nm. At pH 6.5, 25", the midpoints of the Gdn. HCI denaturation curves are 1.89 M Gdn. HC1 for Candida, 2.42 M for horse, and 2.63 M for cow ferricytochromes c . An analysis of these data indicates that cow is a minimum of 650 cal/mol more stable than horse ferricytochrome c and 2300 cal/mol more stable than Candida ferricytochrome c, in the presence of 2-3 M GdneHCI. An analysis of the acid denaturation curves shows that near pH 2.5 at low ionic strength, cow is a minimum of 720 cal/mol
We tested the hypothesis that altered phosphorylation of Ca2+ regulatory proteins contributes to contractile anomalies in cardiac hypertrophy. Cardiac hypertrophy was induced in rats by chronic s.c. administration of isoproterenol (Iso, 2.4 mg/kg/day) via osmotic minipumps. On day 2 of Iso treatment the expression of atrial natriuretic factor was increased, time of relaxation in isolated papillary muscles shortened and protein expression of phospholamban (PLB) and sarcoplasmic reticulum Ca2+-ATPase reduced. In addition, the phosphorylation state of PLB at serine-16 and threonine-17 was decreased from (arbitrary units) 2.3+/-0.3 to 1.1+/-0.2 and from 4.1+/-0.6 to 2.1+/-0.2, respectively. This was not accompanied by altered activity of PLB-phosphorylating protein kinases (protein kinase A or Ca2+/calmodulin-dependent protein kinase II), whereas the activity of types 1 and 2A protein phosphatases (PP1 and -2A respectively) was enhanced from 1.1+/-0.08 to 1.71+/-0.13 nmol/mg/min. Iso treatment did not alter the PP1/PP2A activity ratio and 1 nmol/l okadaic acid, a concentration which completely blocks the catalytic subunit of PP2A, inhibited about 40% of total PP activity in all groups studied. These data indicate that the activity of both PP1 and PP2A were increased. All effects of Iso treatment were abolished by co-administration of propranolol (29.7 mg/kg/day). It is concluded that dephosphorylation of PLB is due to enhanced activity of PP1 and PP2A. We suggest that chronic beta-adrenergic stimulation, which occurs in human cardiac hypertrophy and failure, can lead to increased activity of PPs. This may contribute to altered contractile responses in the hypertrophied heart.
It is suggested that duration of contraction is shorter in human atrium versus ventricle due to the combined effect of decreased PLB levels (which inhibits SERCA function) and increased SERCA levels. The lower relative ratio of PLB to SERCA leads to less inhibition of SERCA and increased Ca(2+)-uptake which enhances relaxation and contraction in human atrium.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.