Volume 20, number 2
MOLECULAR • CELLULARBIOCHEMISTRY
SARCOPLASMIC CALCIUM-BINDING CYCLOSTOME MUSCLE
PROTEINS
IN PROTOCHORDATE
June 28, 1978
AND
CHARACrEmzA~ON OF A NEW PROTEIN tmOM A s m m o x u s
L. KOHLER, J. A. COX and E. A. STEIN*
Department of Biochemistry, University of Geneva, Switzerland (Received November 4, 1977)
Key words: Protochordatemuscle, Cyclostomemuscle, Ca2+-bindingproteins, Amphioxus,Lamprey,Vertebrateinvertebrate junction, Mg2+-binding. Summary
A sarcoplasmic calcium-bindingprotein (SCP) has been purified from the muscle of the protochordate Amphioxus and shown to be more similar to invertebrate SCP's than to their counterpart found in vertebrates, i.e. parvalbumins. The Amphioxus protein has a pI of 4.9, is rich in tyrosine and tryptophan, has a molecular weight of 22,000 and binds strongly 2Ca 2+ with a pK of 7.88. Magnesium competes with calcium for only one of the two metal-binding sites and induces positive cooperativity in C a 2+ binding. In cyclostome muscle (lamprey and hagfish), no protein with high affinity for Ca 2+ or Mg 2+ could be found, irrespective of molecular weight. Instead, a protein with moderate affinity for Ca 2+ (~
MOLECULAR • CELLULARBIOCHEMISTRY
SARCOPLASMIC CALCIUM-BINDING CYCLOSTOME MUSCLE
PROTEINS
IN PROTOCHORDATE
June 28, 1978
AND
CHARACrEmzA~ON OF A NEW PROTEIN tmOM A s m m o x u s
L. KOHLER, J. A. COX and E. A. STEIN*
Department of Biochemistry, University of Geneva, Switzerland (Received November 4, 1977)
Key words: Protochordatemuscle, Cyclostomemuscle, Ca2+-bindingproteins, Amphioxus,Lamprey,Vertebrateinvertebrate junction, Mg2+-binding. Summary
A sarcoplasmic calcium-bindingprotein (SCP) has been purified from the muscle of the protochordate Amphioxus and shown to be more similar to invertebrate SCP's than to their counterpart found in vertebrates, i.e. parvalbumins. The Amphioxus protein has a pI of 4.9, is rich in tyrosine and tryptophan, has a molecular weight of 22,000 and binds strongly 2Ca 2+ with a pK of 7.88. Magnesium competes with calcium for only one of the two metal-binding sites and induces positive cooperativity in C a 2+ binding. In cyclostome muscle (lamprey and hagfish), no protein with high affinity for Ca 2+ or Mg 2+ could be found, irrespective of molecular weight. Instead, a protein with moderate affinity for Ca 2+ (~
