. Biological structure and function; proceedings. Biochemistry; Cytology. 334 JAMES H. C. SMITH ultraviolet radiation. Mr. G. C. McLeod and Miss J. Coomber, in our laboratory [15], discovered that protochlorophyll holochrome irradiated with various ultraviolet wavelengths between 250 and 330 myu, converted only 25 to 30% of the protochlorophyll transformed at 366, 436 m^ (Fig. 7), or with visible light from an electric lamp. If after ultraviolet irradiation, however, the holochrome solution was placed in visible light, the same degree of transformation was achieved as if no previous con- versi
. Biological structure and function; proceedings. Biochemistry; Cytology. 334 JAMES H. C. SMITH ultraviolet radiation. Mr. G. C. McLeod and Miss J. Coomber, in our laboratory [15], discovered that protochlorophyll holochrome irradiated with various ultraviolet wavelengths between 250 and 330 myu, converted only 25 to 30% of the protochlorophyll transformed at 366, 436 m^ (Fig. 7), or with visible light from an electric lamp. If after ultraviolet irradiation, however, the holochrome solution was placed in visible light, the same degree of transformation was achieved as if no previous con- version with ultraviolet had occurred. Wherefore, the ultraviolet at the intensities used had no ill effect on the 300 350 400 Wavelength (my/) 450 Fig. 7. The maximum conversion of holochromatic protochlorophyll to chlorophyll in the range 436 to 250 m/j. The conversion with ultraviolet light could not be explained by proto- chlorophyll absorption else the conversion would have been augmented with longer exposures. But the exposures given were two or three times those necessary to achieve maximum conversion in the 250-330 mn range. The limited action of ultraviolet light may be reasonably explained by assuming the protochlorophyll to be activated through transfer of the energy absorbed by a closely associated amino acid. Only the aromatic amino acids absorb appreciably throughout this range, and of these acids only tyrosine has the proper pK value to correspond with the alkalinities effective in the inhibition of the transformation. From these considerations it is concluded that about 25 to 30% of the protochlorophvll is attached to protein in the holochrome through the tyrosinyl Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original IUB/IUBS International Symposium (1st : 1960 : Stockholm); In
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