The Significance of Respiratory Chain Oxidations 639 



compound with DPNH. Thus it is possible that DPNH and DPN -^ I might not be 

 distinguishable spectrophotomctrically. There is, therefore, no inconsistency between 

 Chance's data and our mechanism. All compounds of the type DPN-A would also 

 be expected to have similar fluorescence spectra. Increased DPN — I formation 

 would be expected to result from the increased DPNH concentration resulting from 

 addition of a-oxoglutarate or glutamate. The formation of DPN ~ I by addition of 

 succinate has already been discussed by Slater (1958). 



In summary, the suggestion of a DPN compound would appear to be consistent 

 with the spectrophotometric and fluorometric data, and to conform with the known 

 chemical properties of DPN. 



Even if A contains an oxidizable hydrogen atom, as in our suggested DPN -^ IH, 

 I cannot see a possibility of a charge-transfer complex in which the reducing equivalents 

 resonate between the two structures: 



DPNH ~1^ DPN ~IH 



since the pyridine ring in DPN-A compounds cannot easily accept an additional 

 hydrogen atom. Thus, it appears that by DPNH ~ I Chance must mean something 

 different from what we mean by DPN '-' IH. 

 Chance: Slater is correct in concluding that he and I have different meanings for the 

 configurations of DPNH ~' I and DPN ~ IH ; our mechanism does not require an "I" 

 group bound in the 4-carbon atom of DPN in order to give DPN ~ I H the spectroscopic 

 properties of DPNH. We wish to include the possibiHty specifically ruled out by 

 Slater, namely an addition compound of DPNH with A or I which could be a protein 

 group in view of the enhanced and shifted fluorescence of mitochondrial DPNH. 



Slater's suggestions that DPNH and DPN ~ I might not be distinguishable spectro- 

 photometrically and that DPN ~I conforms with the known properties of DPN focus 

 particular attention upon experiments in which the increase of absorption at 340 m/< 

 caused by addition of substrates to mitochondria is compared with the diminution of 

 absorption at the same wavelength caused by addition of acetyldehyde and alcohol 

 dehydrogenase to an extract of the mitochondria. Such experiments have been 

 carried out in the two laboratories where they can be appropriately made (see M. 

 Klingenberg, W. Slenczka, and E. Ritt, Biocliein. Z. 332, 47, 1959 and B. Chance and 

 G. Hollunger, Nature, Lond. 185, 666, 1960). 



CONCLUDING REMARKS 



Lemberg: We now come to the end of this week of hard work. My first task is to thank 

 all the contributors who have really made this meeting a success, and the Chairmen 

 of the Sessions who often had quite a hard task to keep us in order. I thanked the 

 organizations which made this meeting possible at the beginning but I have still to 

 thank my colleagues on the Organizing Committee, particularly Prof. Morton and 

 Dr. Falk for the tremendous amount of v/ork they have done which was— as it usually 

 is — far greater than that done by the President. I also thank Prof. Ennor who has 

 been very helpful to us in his capacity as Convener of the National Committee of 

 Biochemistry. Finally, I wish to repeat the thanks which, in the name of the Organizing 

 Committee, I have already conveyed by letters to the Staff of the Australian Academy 

 of Science and of the C.S.I.R.O. for their very valuable help. 



We have moved through a large orbit and varying orbitals, from quantum mechanics 

 to porphyrin and protein chemistry and through biochemistry proper into the realm 

 of biology. Evidently my appeal for brotherly love has been followed and this has 

 contributed to the success of the meeting. Thank you all; we wish you a good and 

 happy journey home or to any other country to which you may go from here. We 

 hope that you have enjoyed your stay in Australia, and that you will come back to us 

 occasionally. 



George: As one of the overseas visitors I wish to express formally our thanks to the 

 Australian Academy of Science for looking after us in such a wonderful fashion. 



Lemberg: I shall have pleasure in conveying this message to the Academy. I now declare 

 the Haematin Enzyme Symposium of the International Union of Biochemistry closed. 



