H

pyridoxal

Figure 2.18 The sequence of steps by which an amino-acid attached to pyridoxal and a decarboxylating enzyme is converted to an amine and C02

is decarboxylated are shown in Figure 2.18. Amines derived from amino-acids are discussed in Chapter 9.

2.2.8 Vitamins

It should be noted in passing that higher animals have lost the ability to synthesize some of the coenzymes or parts of them. By definition, a vitamin is an essential substance that the body cannot make for itself and must acquire through its food. Humans cannot make pantothenic acid (vitamin B5) needed for coenzyme A, nicotinamide (vitamin B3) for NAD+, riboflavin (vitamin B2) for FAD, thiamine (vitamin B[), folic acid (vitamin Be or M) or pyridoxal (vitamin B6). We possess the ability to phosphorylate or otherwise convert the vitamins into active coenzymes. Some of these substances are also vitamins for insects, plus some others which higher animals can make themselves.

2.2.9 Biosynthesis of Formic Acid in Ants

All ants of the subfamily Formicinae have lost the ability to sting but can spray a concentrated solution of formic acid (up to 65% in some species) from their venom glands. Blum and Hefetz (Science, 1978, 201, 545) studied the biosynthesis and showed by using radio-labelled compounds that the formic acid can be formed from serine (CH2OHCHNH2COOH) or glycine (CH2NH2COOH) with the help of tetrahydrofolic acid (Figure 2.19). Apparently any compound capable of contributing a Cx fragment can be a potential source of formic acid. The four enzymes necessary for these steps were all shown to be present in the venom gland. Other insects, including the larvae of the lepidopteran Schizura concinna and many beetles of the family Carabidae and some other arthropods also make and use formic acid in defensive or offensive secretions.

labelled serine

t 1 I5J

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