bk-1985-0276.ch017

17 Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on June 24, 2016 | http://pubs.acs.org Publication Date: April 26, 1985 | doi: 10.1021/bk-1985-0276.ch017

Propionate and Methyl Malonate Metabolism in Insects GARY J. BLOMQUIST, PREMJIT P. HALARNKAR, and LAWRENCE A. DWYER Department of Biochemistry, University of Nevada, Reno, NV 89557

Insects utilize propionate and methylmalonate in the biosynthesis of ethyl branched juvenile hormones and methyl branched cuticular hydro carbons. The sources of propionate and methyl malonate in some insects appear to differ from those in mammals. Succinate is the precursor of propionate and methylmalonate in a termite, whereas valine and probably other amino acids are the sources of propionate and methylmalonate in several other species. An unusual pathway for propionate metabolism has been shown to occur in insects and it may be related to the absence or low levels of vitamin B found in many species. Propionate is converted directly to acetate with carbon 1 of propionate lost as CO , carbon 2 of propionate becoming the methyl carbon of acetate and carbon 3 of propionate becoming the carboxyl carbon of acetate. This pathway suggested the possibility that 2-fluoropropionate might be selectively metabolized in insects to the toxic 2-fluoroacetate. However, preliminary data indicate that 2-fluoropropionate is not toxic to the housefly or the American cockroach. 12

2

P r o p i o n a t e s e r v e s s e v e r a l unique and important r o l e s i n i n s e c t s . I t i s used by some i n s e c t s , i n v e r y s m a l l amounts, as a p r e c u r s o r t o homomevalonate which i s an i n t e r m e d i a t e i n t h e b i o s y n t h e s i s o f j u v e n i l e hormone (JH) I I (1,2) and p r o b a b l y JH I and JH 0 as well. Much l a r g e r amounts o f p r o p i o n a t e and methylmalonate a r e needed f o r t h e b i o s y n t h e s i s o f methyl branched hydrocarbons which a r e major c u t i c u l a r components i n most o f t h e a p p r o x i m a t e l y 100 i n s e c t s p e c i e s whose c u t i c u l a r l i p i d s have been examined ( 3 - 7 ) . U n t i l r e c e n t l y , t h e r e was l i t t l e i n f o r m a t i o n a v a i l a b l e on e i t h e r the s o u r c e o f p r o p i o n a t e o r i t s metabolism i n i n s e c t s . I n mammals v i t a m i n i s a k e y c o f a c t o r i n p r o p i o n a t e and methylmalonate metabolism ( 8 - 9 ) . Recent o b s e r v a t i o n s t h a t some i n s e c t s p e c i e s l a c k o r c o n t a i n low l e v e l s o f v i t a m i n B,« ( 1 0 )

Library 1155 16th St., N.W. Washington, D.C. 20036

Hedin et al.; Bioregulators for Pest Control ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

BIOREGULATORS FOR PEST CONTROL

246

r a i s e d q u e s t i o n s as t o how t h e s e i n s e c t s p e r f o r m o r circumvent such r e a c t i o n s . E v i d e n c e i s p r e s e n t e d i n d i c a t i n g t h a t i n s e c t s have a n o v e l pathway f o r p r o p i o n a t e m e t a b o l i s m as compared t o vertebrates. Sources o f p r o p i o n a t e and methylmalonate and t h e i r u t i l i z a t i o n as s u b s t r a t e s f o r JH and methyl branched h y d r o c a r b o n b i o s y n t h e s i s a r e reviewed.

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on June 24, 2016 | http://pubs.acs.org Publication Date: April 26, 1985 | doi: 10.1021/bk-1985-0276.ch017

Sources of Propionate

and M e t h y l m a l o n a t e

I n v e r t e b r a t e s , t h e major s o u r c e s o f p r o p i o n a t e and m e t h y l malonate a r e odd c h a i n f a t t y a c i d s and t h e amino a c i d s i s o l e u c i n e , v a l i n e and m e t h i o n i n e ( 8 , 9 ) . In the termite Z o o t e r m o p s i s a n g u s t i c o l l i s , which c a n i n c o r p o r a t e p r o p i o n a t e a s the m e t h y l branch u n i t o f mono- and d i m e t h y l a l k a n e s (]_) these s o u r c e s were c o n s i d e r e d u n l i k e l y because t h e d i e t o f t e r m i t e s presumably c o n t a i n s l i t t l e f a t t y a c i d and Z. a n g u s t i c o l l i s c o n t a i n s v e r y s m a l l amounts o f odd c h a i n l e n g t h f a t t y a c i d s (Chu and B l o m q u i s t , u n p u b l i s h e d ) . L i k e w i s e , t e r m i t e s would be e x p e c t e d t o c o n s e r v e e s s e n t i a l amino a c i d s such as t h e ones t h a t c o u l d s e r v e as p r e c u r s o r s t o p r o p i o n a t e and m e t h y l m a l o n a t e . y

A s e r i e s o f e x p e r i m e n t s werç^performed i n ^ h i c h t h e jin v i v o i n c o r p o r a t i o n o f [ 1 - C ] - , [ 2 , 3 - C ] - and H]succlnates into m e t h y l branched a l k a n e s were compared. [ 1 - C ] S u c c i n a t e w^s p r e f e r e n t i a l l y i n c o r p o r a t e d i n t o t h e normal a l k a n e s and [2,3- H ] s u c c i n a t e was p r e f e r e n t i a l l y i n c o r p o r a t e d i n t o t h e methyl branched alkanes (11). T h i s and o t h e r e v i d e n c e ( 1 1 ) suggested t h a t s u c c i n a t e c o u l d be a p r e c u r s o r t o methylmalonate i n t h i s termite. D i r e c t evidence that t h i s termite could u t i l i z e s u c c i n a t e as the p r e c u r s o r t o methylmalonate was o b t a i n e d by examining e i n c o r p o r a t i o n o f [ 2 , 3 - C 2 ] s u c c i n a t e i n t o m e t h y l a l k a n e s by C-NMR. Carbons 2 and 3 o f s u c c i n a t e were i n c o r p o r a t e d i n t o t h e b r a n c h i n g m e t h y l g r o u p ( s ) and t h e t e r t i a r y c a r b o n s ( s ) o f monoand d i m e t h y l a l k a n e s ( 1 2 ) . These d a t a i n d i c a t e t h a t s u c c i n a t e i s m e t a b o l i z e d t o methylmalonyl-CoA and then i s i n c o r p o r a t e d i n p l a c e o f malonyl-CoA a t s p e c i f i c p o i n t s d u r i n g c h a i n e l o n g a t i o n . Recent e x p e r i m e n t s i n o u r l a b o r a t o r y have u t i l i z e d HPLC t o s e p a r a t e o r g a n i c a c i d s from homogenates o f i n s e c t t i s s u e . M i t o c h o n d r i a l p r e p a r a t i o n ^ from Z. a n g u s t i c o l l i s were a p p a r e n t l y a b l e t o m e t a b o l i z e [2,3- C ] s u c c i n a t e t o m e t h y l m a l o n a t e . Radio a c t i v i t y was r e c o v e r e d i n t h e f r a c t i o n c o r r e s p o n d i n g t o propionate. This i n d i c a t e s that t h i s termite i s able to convert s u c c i n a t e t o p r o p i o n a t e , presumably v i a a methylmalonyl-CoA intermediate. When s u c c i n a t e dehydrogenase was i n h i b i t e d by malonate d u r i n g a m i t o c h o n d r i a l i n c u b a t i o n , t h e c o n v e r s i o n o f s u c c i n a t e t o p r o p i o n a t e was i n c r e a s e d , f u r t h e r i n d i c a t i n g t h a t the m i t o c h o n d r i a l p o o l o f s u c c i n a t e c a n be used t o form methylmalonate and p r o p i o n a t e . The g e n e r a l flow o f c a r b o n i n mammals i s p r o p i o n a t e t o methylmalonate t o s u c c i n a t e , which i s then m e t a b o l i z e d by t r i c a r b o x y l i c a c i d c y c l e enzymes. Thus, t h e f l o w o f c a r b o n i n t h e t e r m i t e appears r e v e r s e d from t h a t o b s e r v e d i n mammals. I n o t h e r i n s e c t s , i n c l u d i n g the h o u s e f l y Musca d o m e s t i c a (13,14) and t h e c o c k r o a c h P e r i p l a n e t a a m e r i c a n a (15,16), s t u d i e s w i t h b o t h r a d i o a c t i v e and s t a b l e i s o t o p e s c l e a r l y showed t h a t s u c c i n a t e was n o t a major p r e c u r s o r t o t h e m e t h y l b r a n c h i n g u n i t .



17.

BLOMQUIST ET AL.

247

Propionate and Methyl Malonate Metabolism

I n t h e s e two s p e c i e s , [ H y a l i n e was r e a d i l y i n c o r p o r a t e d i n t o the branche^ a l k a n e s . A C-NMR e x a m i n a t i o n o f t h e i n c o r p o r a t i o n o f [3,4,5- C ~ ] v a l i n e i n t o t h e branched a l k a n e s o f the h o u s e f l y (13) showed tnajj carbons 3, 4, and 5 were i n c o r p o r a t e d i n t a c t ( a s d e t e r m i n e d by C- C c o u p l i n g ) i n t o t h e b r a n c h i n g methyl c a r b o n , t e r t i a r y c a r b o n , and c a r b o n a d j a c e n t t o t h e t e r t i a r y c a r b o n , respective^. S i m i l a r d a t a were o b t a i n e d when t h e i n c o r p o r a t i o n o f [3,4,5- C ^ ] v a l i n e i n t o 3-methylpentacosane was examined i n the American c o c k r o a c h ( 1 7 ) . Whether o r n o t p r o p i o n a t e i s produced a s an o b l i g a t e i n t e r mediate i n the metabolism o f v a l i n e t o methylmalonyl-CoA has been a s u b j e c t o f c o n t r o v e r s y ( 1 8 ) . Indeed, some t e x t b o o k s s t i l l show t h a t m e t h y l m a l o n i c semialdehyde i s d i r e c t l y o x i d i z e d t o m e t h y l malonyl-CoA ( 1 9 ) . U s i n g s t a b l e i s o t o p e s , B a r e t z and Tanaka ( 1 8 ) have p r e s e n t e d c o n v i n c i n g e v i d e n c e t h a t r a t s c o n v e r t m e t h y l m a l o n i c semialdehyde t o p r o p i o n y l - C o A , which i s then c a r b o x y l a t e d to form methylmalonyl-CoA. I t appears t h a t a s i m i l a r pathway o c c u r s i n the h o u s e f l y and t h e American c o c k r o a c h ( F i g u r e 1 ) . I f m e t h y l m a l o n y l semialdehyde were c o n v e r t e d d i r e c t l y t o methyjmalonyl-CoA, one o f t h e C l a b e l e d methyl groups from [3,4,5- C ~ ] v a l i n e would become t h e f r e e c a r b o x y l carbon o f methylmalonyl-CoA and would then be l o s t as CO^ d u r i n g i n c o r p o r a t i o n i n t o t h e a l k y l chain. The o b s e r v a t i o n t h a t carbons 3, 4 and 5 o f v a l i n e were i n c o r p o r a t e d i n t a c t i n d i c a t e s t h a t t h i s does not happen and t h a t v a l i n e p r o b a b l y i s m e t a b o l i z e d v i a p r o p i o n y l - C o A t o methylmalonyl-CoA ( F i g u r e 1 ) . V i t a m i n B-^ i s a r e q u i r e d c o f a c t o r f o r methylmalonyl-CoA mutase, which i s i n v o l v e d i n p r o p i o n a t e c a t a b o l i s m i n mammals. T h i s f a c t and t h e d i f f e r e n c e s o b s e r v e d i n the p r e c u r s o r s t o p r o p i o n a t e and methylmalonate among i n s e c t s p e c i e s ( T a b l e I ) prompted an e x a m i n a t i o n o f a number o f i n s e c t s f o r v i t a m i n B ^ levels. The t e r m i t e Z. a n g u s t i c o l l i s , which r e a d i l y c o n v e r t s s u c c i n a t e t o methylmalonate, has l a r g e amounts o f v i t a m i n B _ , whereas the American c o c k r o a c h has low l e v e l s and the h o u s e f l y does n o t have d e t e c t a b l e amounts o f v i t a m i n (10)« Thus, both d i e t a r y c o n s i d e r a t i o n s and l e v e l s o f v i t a m i n play a r o l e i n d e t e r m i n i n g the p r e c u r s o r s t o p r o p i o n y l and m e t h y l m a l o n y l derivatives i n insects. 2

m

a

v

Metabolism o f Propionate I t i s w e l l e s t a b l i s h e d t h a t p r o p i o n a t e c a n be u t i l i z e d f o r t h e m e t h y l branch u n i t i n m e t h y l branched h y d r o c a r b o n s i n i n s e c t s ( 4 - 7 ) , and r e c e n t d a t a have shown t h a t the methyl branches a r e i n s e r t e d e a r l y d u r i n g c h a j n e l o n g a t i o n r a t h e r than toward t h e end o f the p r o c e s s (13,16). ^C-NMR a n a l y s i s demonstrated t h a t propionates labeled with C i n e i t h e r t h e 1, 2 o r 3 p o s i t i o n s a r e i n c o r p o r a t e d i n t o the methyl branched a l k a n e s o f i n s e c t cuticular lipids. C-3 o f p r o p i o n a t e becomes t h e b r a n c h i n g m e t h y l c a r b o n , C-2 becomes the t e r t i a r y c a r b o n and C - l t h e carbon a d j a c e n t t o t h e t e r t i a r y c a r b o n (13,16,17) i n t h e s e methyl branched h y d r o c a r b o n s . I n d i r e c t e v i d e n c e from s t u d i e s w i t h r a d i o a c t i v e p r e c u r s o r s suggested t h a t i n a d d i t i o n t o l a b e l i n g the methyl b r a n c h u n i t o f 3-methyl and i n t e r n a l m e t h y l branched h y d r o c a r b o n s , p r o p i o n a t e



Ça NH

c -ce-c-co Y

2


VALINE

HOUSEFLY COCKROACH

i METHYLMALONIC SEMIALDEHYDE —

PROPIONATE-

-

i

—

-

Cy-C^-Ca-S-CoA PROPIONYL-CoA

L*co

9

TERMITE CaO

° 2 ~ 6 "Cy"C0

Cy-C^-Ca-S-CoA

C

co "

C

SUCCINATE

2

METHYLMALONYL-CoA

-v 0 Cy-C32

ACETATE

>

9Ύ

(C3-C ) -C3-Q -(C3-C ) -C3 Y

X

x

y

x

METHYLALKANE

F i g u r e 1. Proposed pathways f o r the metabolism o f p r o p i o n a t e and methylmalonate i n s e l e c t e d i n s e c t s .


2


Isoptera

Diptera

Dictyoptera

Order

Metabolism

a

Unpublished

(10)

(10)

R.

Yes

Yes

Yes

a

Yes (17)

Convert Propionate to Acetate

G.J. and H e i s l e r , C.

V a l i n e (Other a.a.?) (20)

S u c c i n a t e (16)



Source o f Propionate and Methylmalonate

and M e t h y l m a l o n a t e i n I n s e c t s

Blomquist,

Not D e t e c t a b l e (10)

High

Not D e t e c t a b l e (10)

Low

Amounts of Vitamin Β 12-

of Propionate

r e s u l t s , H a l a r n k a r , P.P.,

Cabbage Looper ( L a r v a ) Trichoplusia n i Lepidoptera

Termite Zootermopsis angusticollis

Housefly (Adult) Musca d o m e s t i c a

Cockroach ( A d u l t ) Periplaneta americana

Insect

Table I.

Mito

Mito

Mito

Mito

3

(17)

Subcellular Location



250


c o u l d be c o n v e r t e d t o a c e t a t e and s u b s e q u e n t l y l a b e l the s t r a i g h t c h a j n p o r t i o n o f hydrocarbons ( 7 , 1 1 ) . D i r e c t evidence obtained by C-NMR s t u d i e s i n the J i o u s e f l y (14) and the American cock r o a c h (17) showed t h a t [2γ^ C ] p r o p i o n a t e l a b e l s hydrocarbons i n the same p o s i t i o n s as [ 2 - C J a c e t a t e and t h a t [3γ^ C ] p r o p i o n a t e l a b e l s hydrocarbons i n the same p o s i t i o n s as [1- C J a c e t a t e . These d a t a suggest t h a t p r o p i o n a t e i s c o n v e r t e d t o a c e t a t e w i t h carbon 1 l o s t as C0~, c a r b o n 3 becoming the c a r b o x y l carbon o f a c e t a t e and carbon 2 becoming the methyl carbon o f a c e t a t e . P r o p i o n a t e a l s o s e r v e s as a p r e c u r s o r f o r j u v e n i l e hormone b i o s y n t h e s i s i n Manduca s e x t a ( 1_). The e t h y l branch i n JH I I (and presumably those i n JH I and JH 0) i s d e r i v e d from p r o p i o n a t e which i s i n c o r p o r a t e d i n t o homomevalonate. The da£a p r e s e n t ed by Schooley e_t a_l. (1) on the i n c o r p o r a t i o n o f [2- C ] p r o p i o n a t e d i d not e n t i r e l y f i t the p o s t u l a t e d pathways f o r JH biosynthesis. R a d i o a c t i v i t y from [2- C ] p r o p i o n a t e was r e c o v e r e d i n JH I I I , which l a c k s e t h y l b r a n c h e s , and i t s d e g r a d a t i o n p r o d u c t s , n e i t h e r of which s h o u l d have been l a b e l e d . Radioactivity was a l s o found i n d e g r a d a t i o n p r o d u c t s o f JH I I from p o r t i o n s o f the m o l e c u l e t h a t s h o u l d not have been l a b e l e d by p r o p i o n a t e . It was s u g g e s t e d t h a t o t h e r , u n s p e c i f i e d , m e t a b o l i c pathways f o r p r o p i o n a t e c o u l d account f o r the l a d l i n g o f JH I I I by [2- C ] p r o p i o n a t e . On the o t h e r hand, [ 1 - C ] p r o p i o n a t e d i d not l a b e l JH I I I , but d i d l a b e l JH I I i n the p a t t e r n e x p e c t e d . These r e s u l t s c o u l d be e x p l a i n e d i f , as was s u g g e s t e d by the d a t a of D i l l w i t h e t a l . ( 1 4 ) , t h e r e i s a pathway i n which p r o p i o n a t e i s d i r e c t l y c o n v e r t e d t o a c e t a t e w i t h the l o s s o f carbon 1 and the o x i d a t i o n of c a r b o n 3. With a pathway of t h i s t y p e , p r o p i o n a t e l a b e l e d i n carbon 1 would l o s e i t s l a b e l i f i t were c o n v e r t e d t o a c e t a t e p r i o r t o i n c o r p o r a t i o n i n t o o t h e r compounds. However, i f p r o p i o n a t e were l a b e l e d i n carbon 2 or carbon 3 i t would r e t a i n i t s l a b e l upon c o n v e r s i o n t o a c e t a t e . Therefore, any l a b e l i n c o r p o r a t e d i n t o JH o r h y d r o c a r b o n from p r o p i o n a t e l a b e l e d i n carbon 1 would have t o be the r e s u l t of p r o p i o n a t e b e i n g u t i l i z e d as an i n t a c t u n i t . I n c o r p o r a t e d l a b e l from p r o p i o n a t e l a b e l e d i n c a r b o n 2 o r c a r b o n 3 c o u l d r e s u l t from d i r e c t i n c o r p o r a t i o n o f p r o p i o n a t e or from c o n v e r s i o n o f p r o p i o n a t e t o a c e t a t e p r i o r t o b e i n g u t i l i z e d f o r JH o r h y d r o c a r b o n b i o s y n t h e s i s . Thus, the l a b e l i n g p a t t e r n s seen by S c h o o l e y , ejt a l . (1) and D i l l w i t h , e t a l . (14) c o u l d be the r e s u l t o f the r e t e n t i o n o f l a b e l from carbon 2 or carbon 3 of p r o p i o n a t e , and the l o s s of l a b e l from c a r b o n 1 of p r o p i o n a t e d u r i n g the c o n v e r s i o n of p r o p i o n a t e t o a c e t a t e . In v i v o and i n v i t r o s t u d i e s i n our l a b o r a t o r y have d i r e c t l y demonstrated t h a t such a pathway does take p l a c e i n i n s e c t s and may r e p r e s e n t a major pathway f o r the d e g r a d a t i o n ^ o f p r o p i o n a t e . F o l l o w i n g i n j e c t i o n o f [ 1 - C ] p r o p i o n a t e o r [2- C ] p r o p i o n a t e , i n s e c t s were k i l l e d , homogenized, o r g a n i c a c i d s e x t r a c t e d and s e p a r a t e d by HPLC, and r a d i o a c t i v i t y i n each f r a c t i o n ^ g s s a y e d by l i q u i d s c i n t i l l a t i o n c o u n t i n g . Radioactivity from [ 2 - C ] p r o p i o n a t e was r e c o v e r e d i n a c e t a t e as w e l l as i n c i t r a t e and s u c c i n a t e . I n v i v o and i n v i t r o s t u d i e s , as a f u n c t i o n o f t i m e , i n d i c a t e d t h a t p r o p i o n a t e was f i r s t c o n v e r t e d to a c e t a t e which s u b s e q u e n t l y l a b e l e d J j i c a r b o x y l i c a c i d i n t e r m e d i a t e s . R a d i o a c t i v i t y from [ 1 - C ] p r o p i o n a t e was not



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found i n a c e t a t e or any TCA i n t e r m e d i a t e . These r e s u l t s were e s s e n t i a l l y the same i n a l l f o u r of the i n s e c t s p e c i e s s t u d i e d t o date ( T a b l e I ) . The r a t e o f c o n v e r s i o n o f p r o p i o n a t e t o a c e t a t e v a r i e d w i t h i n s e c t s p e c i e s and o c c u r r e d m o s t ^ r a p i d l y i n the h o u s e f l y where about 50% of the i n j e c t e d [ 2 - C ] p r o p i o n a t e was c o n v e r t e d t o a c e t a t e w i t h i n 5 min. S u b c e l l u l a r l o c a l i z a t i o n o f the p r o p i o n a t e t o a c e t a t e pathway was examined i n the h o u s e f l y , t e r m i t e , American c o c k r o a c h and cabbage l o o p e r . I n a l l f o u r s p e c i e s the m i t o c h o n d r i a l f r a c t i o n had s i g n i f i c a n t a c t i v i t y whereas the m i c r o s o m a l f r a c t i o n (105,000g p e l l e t ) and s o l u b l e f r a c t i o n (105,000g s u p e r n a t a n t ) d i d not c o n v e r t p r o p i o n a t e t o a c e t a t e t o any a p p r e c i a b l e e x t e n t . These r e s u l t s were s i m i l a r t o r e s u l t s o f work done i n p l a n t s , which showed t h a t p r o p i o n a t e i s m e t a b o l i z e d t o a c e t a t e (20,21) by mitochondrial preparations. A pathway f o r c o n v e r t i n g p r o p i o n a t e t o a c e t a t e i s not unique i n b i o l o g i c a l systems. P l a n t s , many of which a p p a r e n t l y do not contain vitamin B ^ » convert propionate d i r e c t l y to acetate v i a a 3-hydroxypropionate intermediate (22). The f i n d i n g t h a t many i n s e c t s e i t h e r do not have d e t e c t a b l e l e v e l s of B.^ have v e r y low l e v e l s (10) suggests t h a t , l i k e p l a n t s , i n s e c t s have e v o l v e d an a l t e r n a t i v e r o u t e o f p r o p i o n a t e c a t a b o l i s m . The c o n v e r s i o n of p r o p i o n a t e t o a c e t a t e may be a g e n e r a l pathway i n i n s e c t s , as even the t e r m i t e Z_. a n g u s t i c o l l i s , which has l a r g e amounts o f v i t a m i n B ^ » has t h i s pathway. P r e s t w i c h and coworkers (23,24) have shown t h a t by j u d i c i o u s l y p l a c i n g f l u o r i n e s on s e l e c t e d p o s i t i o n s of f a t t y a c i d s and s t e r o l s ' , i n s e c t s w i l l m e t a b o l i z e the f l u o r i n a t e d p r e c u r s o r t o the potent t o x i n 2 - f l u o r o a c e t a t e ( 2 5 ) . Because i n s e c t s c o n v e r t p r o p i o n a t e t o a c e t a t e , i t was p o s s i b l e t h a t they might c o n v e r t 2 - f l u o r o p r o p i o n a t e t o 2 - f l u o r o a c e t a t e by the same pathway. However, p r e l i m i n a r y e x p e r i m e n t s u s i n g h o u s e f l i e s and c o c k r o a c h e s i n d i c a t e d t h a t 2 - f l u o r o p r o p i o n a t e was not r e a d i l y c o n v e r t e d t o 2 - f l u o r o a c e t a t e . H o u s e f l i e s i n j e c t e d w i t h 2 - f l u o r o p r o p i o n a t e (3 p g / i n s e c t ) were not a f f e c t e d a f t e r 1.5 h r , whereas c o n t r o l i n s e c t s i n j e c t e d w i t h 2 - f l u o r o a c e t a t e (2 y g / i n s e c t ) were a l l dead w i t h i n 0.5 h r . S i m i l a r r e s u l t s were o b t a i n e d w i t h the American cockroach. o

r

Summary P r o p i o n a t e i s a key i n t e r m e d i a t e i n JH and h y d r o c a r b o n b i o synthesis i n insects. I t s e r v e s as a p r e c u r s o r f o r m e t h y l branched h y d r o c a r b o n s which i n many i n s e c t s a r e important com pounds f o r communication and c u t i c u l a r p r o t e c t i o n , and i t i s a p r e c u r s o r f o r j u v e n i l e hormone b i o s y n t h e s i s (JH 0, JH I and JH II). Sources of p r o p i o n a t e have been shown t o be s u c c i n a t e i n a t e r m i t e and c e r t a i n amino a c i d s such as v a l i n e i n o t h e r s p e c i e s . I n s e c t s have an u n u s u a l pathway f o r c a t a b o l i z i n g p r o p i o n a t e which may be r e l a t e d t o the absence or low l e v e l s of v i t a m i n B^ found i n many s p e c i e s . The p r o p i o n a t e to a c e t a t e pathway i s p r e s e n t i n a l l i n s e c t s which have been s t u d i e d , i n c l u d i n g the t e r m i t e , which has h i g h l e v e l s of v i t a m i n Β ^ · The p r e s e n c e o f t h i s u n u s u a l m e t a b o l i c pathway f o r p r o p i o n a t e metabolism o f f e r e d the p o t e n t i a l f o r s e l e c t i v i t y i n d e v e l o p i n g i n s e c t c o n t r o l



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a g e n t s . The compound 2 - f l u o r o p r o p i o n a t e seemed t o be an i d e a l candidate. U n f o r t u n a t e l y , i t was not t o x i c t o the h o u s e f l y o r American c o c k r o a c h , presumably because i t was not m e t a b o l i z e d t o fluoroacetate at a s u f f i c i e n t rate. N o n e t h e l e s s , e x p l o i t a t i o n of unique m e t a b o l i c pathways i n i n s e c t s o f f e r s the p o t e n t i a l f o r novel c o n t r o l techniques.


Acknowledgments Supported i n p a r t by the S c i e n c e and E d u c a t i o n A d m i n i s t r a t i o n of the U.S. Department o f A g r i c u l t u r e under Grant 83-CRCR-1-1210 from the C o m p e t i t i v e R e s e a r c h G r a n t s O f f i c e . A c o n t r i b u t i o n of the Nevada A g r i c u l t u r e Experiment S t a t i o n .

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