Two Heavy Chains of 21S Dynein from Sea Urchin Sperm Flagella1

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Abstract
The biochemical properties of 21S dynein derived from sea urchin sperm flagella and of its components dissociated by low salt treatment were studied. SDS-urea gel electrophoresis and two-dimensional gel electrophoresis showed that the 21S dynein preparation contains two distinct heavy chains. These two heavy chains, termed Aα and Aβ, had apparently the same molecular weight of 500,000 but showed different mobilities on SDS-urea gels. The isoelectric points of Aa and Ab heavy chains were 5.7 and 5.2, respectively, in the presence of urea. Proteolytic digestion patterns of these two heavy chains were clearly different, but the amino acid compositions were similar. Low salt treatment and sucrose density gradient centrifugation could partially separate the components of 21S dynein into two fractions: the one with larger sedimentation coefficient contained the Aα heavy chain, and the other with smaller sedimentation coefficient contained the Aβ heavy chain and three intermediate chains. These two fractions showed distinctly different kinetic properties, and thus may play different roles in dynein-microtubule interaction.