Isolation and characterization of myoglobin and its two major isoforms from sheep heart

We isolated myoglobin from sheep heart by homogenizing cardiac muscle in 70%-saturated ammonium sulfate, followed by chromatography on a column containing carboxymethyl(CM)-Sephadex gel. Two major isoforms of myoglobin, designated Mb 7.9 and Mb 8.1, were separated by chromatofocusing and were distinguished by their different patterns seen on either isoelectrofocusing or on electrophoresis on polyacrylamide gel. The isoelectric points of the major bands of Mb 7.9 and Mb 8.1 were 7.4 and 7.16, respectively. Both isoforms were identical in size when examined by gel filtration chromatography but differed slightly when analyzed by polyacrylamide gradient gel in the presence of sodium dodecyl sulfate. The Mr of Mb 7.9 (15,900 Da) is slightly smaller than that of Mb 8.1 (18,400 Da). When reacted against rabbit anti-sheep myoglobin, two isoforms also appeared as two nonidentical precipitin lines on agarose gel.