Chapter 6, Note 5. Position Of The Double Bond In Monoethenoids

The comparative analysis of the principal naturally occurring mono ethenic fatty acids has shown a curious configuration due to the peculiar relative position of the double bond in these molecules. Figure 245 shows the position of this double bond in the principal monoethenoids. (267) Andre has shown that the double bond is more often placed so as to separate a group of 9 carbons ending with the carboxyl. We could show that this group is present toward the extremity ending with the carboxyl especially if the chain has 18 carbons or less. For the longer chain, this group of 9 carbons is present but usually toward the extremity, ending with the methyl. The importance of this configuration for the Knoop beta oxidation of these acids is discussed in the previous Note.

Similar separation in groups of carbons totaling 9 carbons, are seen in polyunsaturated fatty acids. (Fig. 246)

Chapter 6, Note 6. Saturation—Desaturation Balance In The Liver

The total number of double bonds does not change in the simultaneous processes of saturation and desaturation occurring in the liver. To a preparation of liver cells, saturated and polyunsaturated fatty acids were added. The iodine number of the fatty acid mixture present was determined, as well as the quantity of mono unsaturated members. After incubation at 37°C, the amount of monoethenic members was seen to have increased greatly. Analysis of the total fatty acids present in the preparation, however, showed the same iodine number, indicating that in the changes which had taken place, the saturation and desaturation processes had compensated each other through a transfer of double bonds from the polyunsaturated to the saturated members.

Position Of The Double Bond In Monoethenic Fatty Acids

Principal naturally existing monoethenoids

Fig. 245. Principal naturally existing monoethenoids show that for the members with a short carbon chain the double bond separates a group of 9 carbons toward the end of the molecule having the carboxyl. For fatty acids with more than 18 carbons, the group of 9 carbons separated is toward the end with the methyl group.

In the polyethenoids, groups of 9 carbons are recognized

Fig. 246. In the polyethenoids, groups of 9 carbons are recognized, formed usually by the sum of two or three groups, multiple of 3 (3 or 6). The group of 9 carbons is usually placed toward the methyl end of the molecule.