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Proceedings of the First Symposium on Marsupials in New Zealand

Topic 4: Statements On The Use Of Sequential Fractional Analysis And Protein Electrophoresis In Marsupial Research

page 248

Topic 4: Statements On The Use Of Sequential Fractional Analysis And Protein Electrophoresis In Marsupial Research

CUMMINS. We shall now hear from two Victoria University people who are not working directly on marsupials, but who have something to say on their research programmes that might be of interest to this symposium. The first speaker is Warren Johnston of the Botany Department.

JOHNSTON. Through the good services of Dr Kear and Mrs Fitzgerald samples of forest plants have been collected every 3 months over a 2 year period. Eight of these were known to be eaten by possums, six were known not to be eaten by possums. Now any organism can only exist in an environment because of what is available to it in terms of nutrients. Now how does one analyse for available nutrients? You can do a total analysis of leaf material of any plant you like, and then quote, say, a calcium figure. That calcium figure does not mean that all calcium is available; for instance, a lot may be present as calcium oxylate which is so unavailable, it's not even funny.

To tackle this problem we have a technique we call S.F.A. - sequential fractional analysis. With this technique we run plant material through a series of fractionations in a set chemical sequence; we take each particular extract and analyse it for potassium, calcium, magnesium, sodium, iron, copper, zinc and so on. At the end we have a total figure for, say, calcium; we know, or at least we have a very good idea, that the calcium present in certain fractions is available, whereas the calcium present in other fractions on chemical grounds we believe unavailable. So therefore at the end of the analysis we can estimate how much of that calcium is available. We can arrive at this figure because digestion is a chemical process. Inorganic elements are neglected all the time in nutritional work. You will get far more work done on proteins and carbohydrates but you try to look for figures on available iron, calcium, or copper: they often just don't exist. This is because I do not think people have had a method. Now I'm not going to say that the method we use is 100% effective, but it is at least one step on the ladder, so to speak, to achieving some idea of available nutrients.

Now there are lots of things that could possibly come out of this. It would be the first time in New Zealand that anyone has sat down and analysed our native vegetation for inorganic elements; and, who knows, among the plants that the possum avoids for instance, there might be some with high nitrate page 249 content. You know as well as I do that nitrate is reduced to nitrite and this combines with haemoglobin; this has poisoned quite a few people already since civilisation started. When you look at some analyses of even common vegetables, such as celery or carrot, they're so incredibly high in nitrate that it's not even funny; there have been cases of infants poisoned for instance by carrot juice because of the high nitrate content.

So this is what we are attempting to do. I don't know how successful we will be; it may take us 18 months, or 2 years to complete analysis. To my mind this is the only way to start looking at the inorganic elements that are required by an animal.

CUMMINS. Thank you Warren, I think that will be a matter of interest to a number of people here interested in nutrition, palatability of bait, and so on. We now have Peter Harper who is doing work on protein analysis. This might be of interest to people who are looking at aspects of disease or speciation in possums or wallabies.

HARPER. I have been looking at the plasma proteins of albatrosses and petrels using acrylamide vertical-slab gel electrophoresis in conjunction with immuno-electrophoresis.* With colleagues in the Botany and Zoology Departments we have developed a technique using some relatively inexpensive components and are resolving in the order of 22–24 different proteins in this sea-bird plasma. Runs I have done on human plasma reveal quite astonishing numbers of proteins. It is a simple, inexpensive technique that gives beautifully reproductive results. I pass on the information to you in case you wish to examine genetic polymorphism in marsupials. It is a very exciting and interesting tool to use.

* this work is now published in NZ Journal of Zoology, 1978, Vol. 5, 509–548 - Editor.