178 



J. E. O'Hagan 



of the dithionite. The first curve was obtained after standing 3 hr, dithionite 

 added at the same concentration as for the iron porphyrins, and the solutions 

 stood another 3 hr to give the second curve. The shght difference is due to the 



Fig. 1 . Attachment of metalloporphyrins to human serum albumin. 



(a) Soret absorbance increment (A) curves prepared, as described in the text, for 

 haematin + human serum albumin at 404 m/n • — • — •, for haem + human 

 serum albumin at 414 m/n O— O — O. 



(b) Soret peak absorbance increment curves for nickel mesoporphyrin + human 

 serum albumin at 394 m/t before A — ▲ — ▲ and after ■ — ■ — b adding di- 

 thionite. (Buffers, pH 4-0-6-2 phthalate, pH 6-2-7-2 phosphate, I = 0-05, 



T = 2rc.) 



decreased value for the metalloporphyrin (without albumin) which is not in 

 true solution and whose absorbance is decreasing with time. It was concluded 

 that reduction significantly decreased the acid strength of at least one of the 

 haematin propionate groups. 



Attachment of Haematin and Haem to Caffeine 



Caffeine was found by J. Keilin (1943) to combine with copper uroporphyrin 

 III and with manganese mesoporphyrin, but she detected no reaction between 

 haematin and caffeine. This seemed unusual and O'Hagan and George 

 (unpubhshed, quoted by O'Hagan and Barnett, 1958) found attachment at 

 pH 11-3 (1-33 mol of caffeine/mol of haematin) and also at pH 7-0 (stoichio- 

 metric relationship not determined). This suggested stronger attachment of 

 haematin than haem to caffeine since J. Keilin had found at least 20 mol of 

 caffeine/mol of haem to be required for caffeine-haem formation at high pH. 



A saturated solution of caffeine (about 10~i m) was substituted for the 

 albumin in the experiments reported above and the absorption increments 

 plotted as shown in Fig. 2. The peaks for the ferrihaemcaff'eine and ferro- 

 haemcafifeine were 402 and 420 mju respectively. Nickel mesoporphyrin also 



