The reaction kinetics of the enzymatic synthesis of cephalexin from 7-aminodeacetoxy cephalosporanic acid and phenylglycine methylester was studied using the synthesizing enzyme obtained from Xanthomonas citri. The activation energy, Km values for 7-aminodeacetoxy cephalosporanic acid and phenylglycine methylester, and Ki value for phenylglycine methylester were determined as 8.63 kcal/mol, 3.7mM, 14.5mM, and 70mM, respectively. The enzyme was found to be constitutive and susceptible to deactivation.

SummaryA system of automatic control of substrate inflow into an aerated culture of microorganisms which depend on oxygen-absorption rate (OAR) has been devised and tested. As the control variable, dissolved oxygen concentration (DOC), which shows the equilibrium between OAR and oxygen-uptake rate in the microbial culture, was chosen. If the equilibrium is disturbed by changes in OAR, then the oxygen-uptake rate is changed by substrate limitation. The DOC is measured by means of a Clark-type polarographic electrode, and the signal is used to actuate the substrate inflow valve or pump. The oxygen-uptake rate changes of microorganisms, after the addition or exhaustion of substrate in the medium, are so rapid that they can be used for this type of control.Fundamental equations were derived and graphical solutions for the control system parameters were suggested for the steady-state relations between DOC, oxygen-uptake rate, specific growth rate, substrate concentration, KLU, and conrentration of microorganisms. The system is stable in the entire range of the uptake rates up to nearly the maximum attainable in unlimited substrate conditions, and can be operated in batch feed or continuous flow modifications. It was experimentally tested with the yeast Saccharomyces cerevisiae. The complete utilization of aeration-system capacity of the fermentor was achieved with high yeast yield arid no alcohol formation. The quality of the product was excellent.

SummaryUsing continuous and fed-batch penicillin fermentation systems some important metabolic parameters have been determined for the purpose of achieving process improvement and better process control. The specific uptake rates determined under the optimal conditions are: 0.33 mmol hexose/g cell/hr, 1.6 mmol oxygedg celYhr, 2 mg NH,-nitrogedg cell/hr, 0.6 mg PO,phosphorus/g cell/hr, 2.8 mg SO,-sulfur/g celYhr, 1.8 mg phenyl acetic acid/g celYhr. It was also found that during the production phase, or idiophase, the specific growth rate should be maintained at about 0.015 hr-I in order to support the maximum penicillin productivity of the given strain. Based on the results of this study a significant process improvement has been achieved through proper control of the supply and demand of the important nutrients and oxygen.

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