Heat-labile bodies

Materials produced by crystalliferous bacilli which elicit a toxic response in susceptible insects may be separated into two types. The first type, the true toxins, include the crystalline protein inclusion body the parasporal body of Hannay (14)], a heat-stable, water-soluble exotoxin active against flies, a heat-stable, dialyzable water-soluble exotoxin, toxic to Lepidoptera on injection (23), and a heat-labile, water-soluble, filterable exotoxin, toxic toward larch sawfly larvae (Hymenoptera) which was reported by Smirnoff (31). 

In general, pyridoxamine and pyridoxin are more stable than pyridoxal. All vitamers are relatively heat-stable in acid media, but heat labile in alkaline media. All forms of vitamin B6 are destroyed by UV light in both neutral and alkaline solution. The majority of vitamin B6 in the human body is stored in the form of pyridoxal phosphate in the muscle, bound to glycogen phos-phorylase. 

Complement comprises a group of heat-labile serum proteins which, when activated, are associated with the destruction of bacteria in the body in a variety of ways. It is present in low concentrations in serum but, as its action is linked intimately with a second (specific) set of defence mechanisms, its composition and role will be dealt with later in the chapter. 

The most potent mucosal adjuvants have been shown to be the toxins derived from Vibrio cholerae or Escherichia coli, which should not be surprising since these organisms invade the body through the GI tract. Obviously too toxic for human use because they are the source of cholera or diarrhoea, heat labile enterotoxins have been tested in mice and shown to be potent adjuvants for orally or nasally administered influenza vaccine. The potency of heat-labile enterotoxin mutants may also be enhanced by formulation into bioadhesive particulate delivery systems, and this is an area under current exploration. 

Ascorbic acid (vitamin C), the antiscurvy vitamin, is used by the body to form and maintain intercellular and skeletal material such as the collagen of fibrous tissue and the matrix of bone, dentin, and cartilage. Milk and milk products are not considered a significant source of this vitamin and should not be relied upon as such. Freshly drawn cow s milk contains about 2 mg ascorbic acid per 100 g milk, but as vitamin C is heat labile and easily destroyed by oxidation, the vitamin C content of pasteurized milk is reduced to about 0.94 mg/100 g. 

A cigarette made from tobacco will contain about 1 to 2 milligrams of nicotine. Because nicotine is quite volatile and heat labile, only about 20% of it is actually inhaled into the body. However, because of its exceptional lipid solubility, at least 90% of the inhaled nicotine is absorbed into the body. Nicotine can also be rapidly absorbed by the mouth or intact skin. Once the smoke is inhaled, absorption via the lungs and transport to the brain occurs within 2 to 7 seconds. This makes smoking tobacco as efficient as an intravenous injection in terms of getting nicotine to its site of action within the brain. This speed of entry into the body may also underlie why nicotine is so toxic. Sixty milligrams is considered a lethal dose for a human death takes only a few minutes to occur and results from a loss of control of the nicotinic receptors on the diaphragm muscles. 

Tyrosine can also be acted on by the enzyme tyrosinase and converted into a dark pigment. This enzyme is quite interesting to study because it is vulnerable to a genetic mutation that makes it heat labile (i.e., it only works correctly in the cooler areas of the body). The consequence of this mutation is a lack of pigmentation in humans (albinism) and, conversely, the characteristic pattern of dark pigmentation at the ends of the nose,... 

The hydroperoxide cleavage enzyme from cucumber fruit is optimally active at pH 6.5, is very heat-labile, and attacks both 9- and 13-hydroperoxide isomers with equal facility. Subcellular localization studies have shown that the enzyme is associated mainly with the plasmalemma, Golgi body, and endoplasmic reticulum membranes (Wardale et al., 1978). 

In cases of face or body involvement, hot moist compresses or irrigation with heated fluids can be employed (the heat may have an attenuating effect on the heat-labile components of the venom)... 

The term atopy was introduced by Coca and Cooke in 1923 (3). They reported the presence of heaHabile bodies, which they called reagins by virtue of their similarity in this respect to the heat-labile reagins (complement) of the Wassermann reaction. They concluded that it is advisable for the present... 

The body of the injector is heated to ensure the sample is volatilized and inside is an inert glass liner. This glass liner helps minimize any sample decomposition that might occur when thermally labile materials come in contact with hot-metal surfaces. The carrier gas enters behind the glass liner and is thus preheated. The sample is injected into the stream of carrier gas that passes down the center of the tube, a portion passes down the capillary column. 

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