Properties and intracellular localization of calpain activator protein.
In this paper, we have further analyzed the properties of calpain activator (CA) in order to better define its physiological function. The activator shows a pH optimum approximately 7.8-8.0, independently of the nature of the buffer used. Although the maximal activity is observed with human acid-denatured globin, the effect of CA is detectable with other protein substrates, such as casein and insulin. A comparable activating effect is observed also with the synthetic substrate Succ-Leu-Tyr-AMC. The activatory effect has been evaluated in a reconstructed system, using plasma membrane Ca(2+)-ATPase as substrate. CA is localized in erythrocyte precursor cells on the inner surface of the plasma membrane in very high amount and its level profoundly decreases up to 10% of the original value when cells reach the terminal differentiated state.
Melloni
E
E
Department of Experimental Medicine-Biochemistry Section, University of Genoa, Italy. melloni@csita.it
Minafra
R
R
Salamino
F
F
Pontremoli
S
S
D000818:Animals; D002021:Buffers; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002154:Calpain / Q000378:metabolism*; D002364:Caseins / Q000378:metabolism; D002454:Cell Differentiation; D004789:Enzyme Activation / Q000187:drug effects; D020536:Enzyme Activators / Q000378:metabolism* / Q000494:pharmacology; D004910:Erythrocyte Membrane / Q000378:metabolism; D004912:Erythrocytes / Q000166:cytology / Q000378:metabolism; D015672:Erythroid Precursor Cells / Q000166:cytology / Q000378:metabolism; D005914:Globins / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007328:Insulin / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism* / Q000494:pharmacology; D051379:Mice; D011489:Protein Denaturation; D011506:Proteins / Q000378:metabolism* / Q000494:pharmacology; D051381:Rats; D013379:Substrate Specificity / Q000187:drug effects; D014407:Tumor Cells, Cultured
D002021:Buffers; D002364:Caseins; D020536:Enzyme Activators; D007328:Insulin; D008565:Membrane Proteins; D011506:Proteins; C410340:calpain activator; D005914:Globins; D002154:Calpain; D000252:Calcium-Transporting ATPases