590 DOWSE, NEUMAN, LANE, AND NEUMAN 



There would seem, considering all the fragmentary data collected 

 here and elsewhere (Cohn and Forscher, 1962a, 1962i>; Lekan et al., 

 1960), to be no reason to doubt the presence of the TCA cycle in 

 bone. In the calvarium it is present from succinate to citrate, and 

 citrate can be further metabolized. The failure to show effects on 

 the Q02 by addition of intermediates is not really surprising, for it 

 is necessary to deplete the endogenous supply of substrate in a 

 tissue before this can be achiev^ed. Subsequent addition of the inter- 

 mediate, then, merely results in a return of the Qo._, to the initial 

 yalue. There is also, in the data presented, no reason to conclude 

 that the oxygen uptake results from s) stems other than the TCA 

 cycle, for in a tissue exhibiting a continuing aerobic glycolysis (see 

 below) the ayailability, of pyruyate at least, for the TCA cycle will 

 not be limiting. 



Glycolysis 



Like other "bone" preparations (Cohn and Forscher, 1962/?; 

 Laskin and Engel, 1956; Borle et a]., 1960fl, 1960/?), calyaria show 

 high rates of glycolysis eyen under aerobic conditions. With no 

 added substrate, glycolysis (defined as lactate production) de- 

 creases with time; with added glucose, the rate is linear for at least 

 3 hours (Fig, 2A). Anaerobicalh', the initial glycolytic rates are 2 

 to 2.5 times higher. Though added glucose maintains the initial rate 

 for 3 hours, in the absence of added substrate the rate falls off even 

 more rapidly than it does aerobically. Thus, after 2 or 3 hours' in- 

 cubation total lactate accumulation is about the same, anaerobically 

 or aerobicall)'. This may account for the failure of some investigators 

 to observe the Pasteur effect (Lekan et ah, 1960). 



When shorter periods of incubation are employed, the effect of 

 oxygen on endogenous glycolysis is readily apparent, as seen in Table 

 IV. Here periods of 30 and 60 minutes were used, and a Pasteur ef- 

 fect of some 70 per cent was found. 



Lactate production increases with increasing concentrations of 

 glucose up to about 4 niM (Fig. 2B). Thereafter the Ql increases 

 less rapidly, especially in the bicarbonate medium. 



A marked effect of the buffer present, seen in Fig. 2B, is further 

 demonstrated in Table IV. In the bicarbonate-buffered medium, the 



