Plasma transport of the 20,000-dalton variant of human growth hormone (20K): evidence for a 20K-specific binding site.

摘要: The 20,000-dalton variant of human GH (20K) is known to circulate in blood, but few details are about its plasma transport. A substantial portion 20K appears be protein bound despite low affinity for the receptor-related GH-binding (BP). We, therefore, investigated binding pattern plasma. Radioiodinated was incubated with or fractions, and mixture fractionated by gel filtration. Saturation/Scatchard analysis performed both 22,000-dalton (22K). majority (approximately 80%) protein-bound complexed a BP (Ka = approximately 2 x 10(5) M-1), remainder high affinity2 BP. specific 20K; it may involve 20K-specific site on previously described (peak I) separate 22K did not interact this site/BP. Analysis 20K-BP complex sodium dodecyl sulfate-polyacrylamide electrophoresis isoelectric focusing suggested, prove, existence 20K. We conclude that binds primarily affinity, (possibly new, third GH-BP), only small fraction This markedly different from 22K, which predominantly site/BP suggests an as yet unrecognized role variant.