Relationship between Photoconvertible and Nonphotoconvertible Protochlorophyllides

The transformation of protochlorophyllide (PChle) into chlorophyllide (Chle) has been studied in isolated etioplasts from Zea mays. ATP (1.5 mM) prevented the transformation of pho- UTP, GTP, and CTP gave 40 to 50% of the ATP response with intact etioplasts. In envelope-free etioplasts, ATP gave the greatest response but the other nucleotides were now 80% as effective as ATP. After primary photoconversion, ATP stimulated resynthesis of PChle 650. It is proposed that ATP both gives the holochrome the ability to bind to the PChle molecule and enables additional association of the pigment-protein complex to form PChle 650.

Section: Methodssupporting

confidence: 81%

The Effect of ATP on the Photoconversion of Protochlorophyllide in Isolated Etioplasts of Zea mays

Horton¹,

Leech²

1975

“…1) is consistent with the hypothesis that ALA-protochlorophyllide must combine with the holochrome apoenzyme before it can be phototransformed (8,11,16). This combination of protochlorophyllide and holochrome apoenzyme has a temperature dependence of the same order as the formation of most other enzyme-substrate complexes.…”

supporting

confidence: 76%

The Abolition of the Lag Phase in Greening Cucumber Cotyledons by Exogenous δ-Aminolevulinic Acid

Castelfranco

Rich²,

Beale³

1974

Etiolated cucumber cotyledons treated with 5-aminolevulinic acid accumulated protochlorophyllide which was phototransformable to chlorophyll(ide). The phototransformation process in the 5-aminolevulinic acid-treated tissue was markedly temperature-dependent, consistent with the view that this protochlorophvllide must combine with the holochrome apoenzyme before phototransformation can occur.The treatment which effects lag phase removal in control tissue did not affect the course of chlorophyll(ide) accumulation in i-aminolevulinic acid-treated tissue under either continuous or intermittent illumination. It was concluded that the lag phase in etiolated tissues must reflect the gradual development of the ability to synthesize 5-aminolevulinic acid at an appreciable rate.

“…24). Sundqvist (23) (2,8,10,11,18,19,(23)(24)(25) indicate that nontransformable PChld' may serve as a precursor of PChldO,H and that the holochrome protein may act as a "photoenzyme" (9,12,25) in the conversion of PChld to Chld, at least in the early stages of greening.…”

Section: Discussionmentioning

confidence: 99%

“…P. and P. can be converted to P., by heat, acid, freezing and thawing, and by treatment with a variety of compounds (4-6, 13). Pe2s is not directly phototransformable to Chld but, under some circumstances, seems to act as a precursorof P. (10,11,18,23,24).…”

mentioning

confidence: 99%

The Conversion of Photoinactive Protochlorophyllide₆₃₃ to Phototransformable Protochlorophyllide₆₅₀ in Etiolated Bean Leaves Treated with δ-Aminolevulinic Acid

Gassman¹

1973

The relationship of phototransformable protochlorophyllide to photoinactive protochlorophyllide has been studied in primary leaves of 7-to 9-day-old dark-grown bean (Phaseolus vulgaris L. var. Red Kidney) seedlings. Various levels of photoinactive protochlorophyllide, absorbing at 633 nm in vivo, were induced by administering 6-aminolevulinic acid to the leaves in darkness. Phototransformable protochlorophyllide, absorbing at 650 nm in vivo, was subsequently transformed to chlorophyllide by a light flash, and the regeneration of the photoactive pigment was followed by monitoring the absorbance increase at 650 nm in vivo. A small increase in the level of protochlorophylliden, causes a marked increase in the extent of regeneration of protochlorphyllidem0 following a flash. High levels of the inactive pigment species, however, retard the capacity to reform photoactive protochlorophyllide. A nonstoichiometric and kinetically complex decrease in absorbance at 633 nm in vivo accompanied the absorbance increase at 650 nm. The half-time for protochlorophyllideusO regeneration in control leaves was found to be three times longer than the half-time for conversion of chlorophyllideom to chlorophyllideos3 at 22 C. The results are consistent with the hypothesis that protochlorophyllidee33 is a direct precursor of protochlorophyllide&0 and that the protein moiety of the protochlorophyllide holochrome acts as a "photoenzyme" in the conversion of protochlorophylide to chlorophyllide.Etiolated leaves of bean seedlings contain at least three species of PChld.' These pigment species can be identified by their absorption maxima in vivo at -196 C in the red region of the spectrum (1,5,15