Phenylalaninylargininylarginine: a novel tripeptide exerting Zn(2+)-dependent, insulin-mimetic inhibitory action on myocardial proteolysis.
A novel tripeptide, Phe-Arg-Arg, was found to exert a potent, insulin-mimetic inhibitory action on lysosomal proteolysis in the Langendorff-perfused rat heart. This tripeptide was synthesized based upon its partial structural analogy to the biguanide anti-hyperglycaemic agent, phenformin (phenylethylbiguanide), which has previously been found to exert a Zn(2+)-dependent inhibitory action on lysosomal proteolysis. Hearts were biosynthetically labelled with [3H]leucine in vitro. The percentage change in subsequent release of [3H]leucine (2 mM non-radioactive leucine) was determined in non-recirculating perfusate. The background Zn2+ content of the perfusate was determined to be 20 nM. Major endogenous Zn2+ buffers were present in molar excess of Zn2+: 0.1 mM citrate, 0.2% BSA, and complete physiological amino acids. Infusion of maximally effective levels of chloroquine (30 microM) or insulin (5 nM) caused a 38% inhibition of total proteolysis, which corresponds to the lysosomal subcomponent. In the presence of background levels of perfusate Zn2+ the infusion of Phe-Arg-Arg (10 microM), insulin (5 nM), or phenformin (2 microM) maximally caused a 39% inhibition of [3H]leucine release. Combined infusion of maximally effective levels of insulin and Phe-Arg-Arg, or maximal levels of chloroquine and Phe-Arg-Arg did not cause additive inhibition of [3H]leucine release greater than the 39% inhibition caused by either agent alone, regardless of the order of infusion. Addition of physiological concentrations of Zn2+ (1 microM) to the background perfusate Zn2+ accelerated the insulin-mimetic action of submaximally effective levels of Phe-Arg-Arg, and increased its potency. Prior chelation of background Zn2+ by a 3 h perfusion with CaNa2 EDTA (2 microM) reversibly delayed the time course of Phe-Arg-Arg action and decreased its potency at submaximal concentrations.
Zhang
L
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Department of Pharmacology and Toxicology, School of Medicine, Wright State University, Dayton, OH 45435.
Lockwood
T D
TD
D000595:Amino Acid Sequence; D000818:Animals; D004492:Edetic Acid; D006321:Heart / Q000187:drug effects*; D006868:Hydrolysis; D007328:Insulin / Q000494:pharmacology*; D007930:Leucine / Q000378:metabolism; D008969:Molecular Sequence Data; D009206:Myocardium / Q000378:metabolism*; D009842:Oligopeptides / Q000494:pharmacology*; D051381:Rats; D015032:Zinc / Q000378:metabolism*
D007328:Insulin; D009842:Oligopeptides; C082640:phenylalanyl-arginyl-arginine; D004492:Edetic Acid; D007930:Leucine; D015032:Zinc