. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 400 450 500 550 600 650 Wavelength (nm) Figure 1. Optical absorption spectra acquired through the anterior region of the isolated notochord of Branchiostama californiense (A) and B. floridae (B) equilibrated with air ( ) and with nitro- gen (- -). In vitro spectra of B. floridae myotome extracts (C) are shown equilibrated with air ( ) and with added sodium dithionite (- -). Specimens of B. californiense were purchased from Pacific Biomarinc Supply Co. (Torrence, CA), and those of B. floridae were collected from shall
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 400 450 500 550 600 650 Wavelength (nm) Figure 1. Optical absorption spectra acquired through the anterior region of the isolated notochord of Branchiostama californiense (A) and B. floridae (B) equilibrated with air ( ) and with nitro- gen (- -). In vitro spectra of B. floridae myotome extracts (C) are shown equilibrated with air ( ) and with added sodium dithionite (- -). Specimens of B. californiense were purchased from Pacific Biomarinc Supply Co. (Torrence, CA), and those of B. floridae were collected from shallow waters on the Gulf of Mexico or purchased from Gulf Specimen Co. (Panacea, FL). nitrogen. Myotome Hb spectra are shown for the sample equilibrated with air or under anoxic conditions produced by addition of sodium dithionite. The air-equili- brated notochord samples show absorbance maxima at 418 nm, 546 nm, and 582 nm (±lnm); the nitrogen- equilibrated samples show absorbance maxima at 435 nm and 556 nm (±1 nm). The dilute /'/; vitro myotome Hb spectra show a distinct Soret band at 416 nm (±1 nm) in air and 430 nm (± 1 nm) with sodium dithionite; however, the visible peaks were below detectable levels. The ob- served absorbance maxima and maxima shifts are revers- ible and are characteristic of the oxygenated and deoxyge- nated states of a typical Hb (11). Another peak occurs at 500 nm in the in situ notochord and in vitro myotome spectra, but this peak does not shift upon changes in oxygenation state and disappears following anion-ex- change chromatographic purification, indicating that it is not a globin-related absorbance (data not shown). These data clearly demonstrate that Hb capable of reversible oxygen binding is expressed in two species of cephalo- chordates, thus expanding the known range of expression among chordates to include nonvertebrate chordates. The size-exclusion chromatography (SEC) elution pro- file at 415 nm for crude protein extract from not
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