Isolation from Spirulina membranes of two photosystem I-type complexes, one of which contains chlorophyll responsible for the 77 K fluorescence band at 760 nm.

Two types of chlorophyll-protein complexes of photosystem I (PSIa, PSIc) have been isolated from the membranes of Spirulina platensis using a Triton X-100 treatment and chromatography on DEAE-Toyopearl. The complexes are equally enriched with P700 (Chl: P700 = 100-110) but show different electrophoretic molecular masses--140 (PSIa) and 320 kDa (PSIc)--and differ in the content of long-wavelength absorbing Chl. PSIa has a typical PSI fluorescence band at 730 nm (F730) as the main band at 77 K, whereas PSIc is responsible for F760, the intensity of which depends on the redox state of P700. PSIc only shows 77 K light-induced variable fluorescence at 760 typical of Spirulina membranes and cells.