I suppose the main reason for my decision to leave the main brunt of work on polynucleotide synthesis and sequence determination to others was that I was still much involved in coenzyme synthesis, and in the development and refinement of procedures for polyphosphorylation which were a prerequisite for it. Furthermore, I was engaged on structural studies on vitamin B12 and in addition to a number of other smaller efforts I was already getting deeply involved in the fascinating problems presented by the remarkable colouring matters present in the haemolymph of aphids. Even although I had for those days a very large research school, there were limitations to what I could tackle!
Following our synthesis of adenosine triphosphate (ATP) our next major triumph in the coenzyme field was the synthesis of flavin-adenine-dinucleotide (FAD) published with G. W. Kenner and S. M. H. Christie in 1952. In the years that followed a variety of other compounds of this type were synthesised including inter alia cozymase (nicotinamide-adenine-dinucleotide) and uridine-diphosphate-glucose. It was, indeed, for my work on phosphorylation and nucleotide coenzymes that I received the Nobel Prize for chemistry in 1957.
Ever since my early work on vitamin B1 in Edinburgh, I retained an interest in the B group of water-soluble vitamins, and did indeed carry out work on some of them in Manchester. One of the most intriguing features of the group was its association with the anaemias. The picture was very confused, and it was not until the 1940s that it became clear that, although such members of the B group as folic acid were involved in nutritional anaemias, the factor involved in pernicious anaemia - the 'external factor' present in liver extracts - was still unisolated. I had not myself taken much interest in pernicious anaemia, and had confined my interest largely to the B vitamins involved in nutritional macrocytic anaemias, but my attention had been drawn to the problem by H. D. Dakin, when I visited him at his home near New York on my way to Pasadena with my wife in 1938. Dakin had been interested in the problem ever since Minot and Murphy in 1926 had shown that whole liver would cure pernicious anaemia, and he had been trying to isolate the material responsible from liver extracts. He had, however, like other workers, made very slow progress indeed since the only way one could test the material was on human patients. Such a test was bound to be inaccurate, but what was (from Dakin's point of view) worse, was that clear cut cases of pernicious anaemia were none too common and clinicians, not unnaturally perhaps, were more interested in curing their patients than in testing Dakin's extracts. When I returned to England I remember discussing the matter with the research group at Glaxo Laboratories Ltd; one of their number, E. Lester Smith, was determined to go ahead on liver extract, and we encouraged him to do so. He slogged on despite every kind of discouragement encountered in the course of testing on human patients and eventually, in 1948, only a very short time after Folkers and his group at the Merck Laboratories in the United States, he did indeed isolate the anti-pernicious anaemia factor Vitamin B12. These two nearly simultaneous isolations of the vitamin were quite independent of one another; but it is remarkable that they should have been so close, when we know that the American group were able to use a microbiological test, while Lester Smith had to go all the way with the much more difficult clinical test procedure. Since I had been associated with the Glaxo isolation work throughout its course, it was perhaps not surprising that I should have been asked if I would undertake a chemical study of it, while Dorothy Hodgkin studied the vitamin by the X-ray method. This I agreed to do, and with my friend and colleague A. W. Johnson we started work. It proved extremely difficult; for one thing we had, during the first year or two of our studies, extremely small amounts of vitamin available to us, and, even more importantly, the molecule proved to be one of almost fantastic complexity. We were able to settle some of its features and learn something about the central part of the molecule by hydrolytic and oxidative studies, but our major contribution lay, perhaps, in the fact that some of our degradation products materially helped Dorothy Hodgkin in her X-ray studies, which in 1955 finally gave the complete vitamin structure. Subsequently, with V. M. Clark, I carried out quite a bit of work on methods which might be applicable to the synthesis of the vitamin, but dropped them, partly because a total synthesis using them would have absorbed a greater part of our research effort than we wished to devote to it, and partly because R. B. Woodward, who had also taken up the synthesis, appeared to me to have a method more likely to succeed (as indeed, with the cooperation of Albert Eschenmoser and his group at Zurich, it ultimately did). A third major topic of research extending over more than twenty years in Cambridge concerned the colouring matters present in the haemolymph of insects belonging to the family Aphididae. My reasons for becoming involved in work on aphid pigments are rather interesting. When I was in Oxford with Robinson I did some work on the colouring matters present in the mycelia of some plant pathogenic fungi of the Helminthosporium group. These colouring matters were derivatives of anthraquinone, and, out of curiosity, I went through the literature and listed all the anthraquinones known to occur in nature together with their source and the pattern of substitution in them. It appeared to me that they seemed to fall very roughly into two groups according to their nuclear substitution - those from higher plants on the one hand, and those from fungi on the other. There were, however, two odd ones obtained from insects - carminic acid from cochineal, and kermesic acid from the oak chermes - which seemed to resemble the fungal anthraquinones rather than those from higher plants. This might not seem very remarkable, but I recalled that these insects belonged to the family Coccididae whose members are known to contain symbiotic fungi located in special cells called mycetomes. Accordingly, I found myself wondering whether it was the insect or the symbiotic fungi that produced the anthraquinone pigments, and I decided I would look into this when I had some time and opportunity. While in Edinburgh I tried to pursue the matter further. It was, of course, necessary for me to obtain supplies of living cochineal insects since examination of the cochineal of commerce would teach me nothing. I soon found, however, that the authorities were not at all enthusiastic about my importing the insects, and the project went into cold storage until 1939. In the early summer of that year, I drove with my wife and some friends from Manchester to Lake Bala in north Wales for a day's outing and we picnicked by the lake hard by a sizeable stand of foxgloves. As I lay dozing after lunch looking up at the foxgloves, I noticed that one of them had a heavy infestation of black aphids on one of the flower heads; and, I thought, ' aphids are zoologically very close to the coccids - perhaps they too have anthraquinones'. So I took a few aphids and rubbed them between my fingers; sure enough, my fingers were stained. But, oddly, the stain was at first yellowish and then after a short time became red (which was the colour expected of an anthraquinone). So I cut the whole head off the infected foxglove, took it back to Manchester, and had a look at the aphids. It was soon clear that the colouring matter in them was not an anthraquinone, and I confirmed the fact that the coloured substance in the insects did undergo a curious change of colour from a kind of khaki to red within a very short time of its extraction. I also went to the entomological literature and found that the Aphididae like the Coccididae contained symbiotic fungi. I decided there and then, that I would leave the Coccididae alone and look at the Aphididae to satisfy my curiosity both as to the nature of their colouring matters and their true origin, i.e. from insect or fungus. But I had to wait until the early summer of 1940 for the next aphid season; by then the war had started in earnest, and I had to put the matter to one side. I resolved to take it up again when the war was over, and so indeed I did.