How can I access serial object without reopening serial in GUI functions

I am writing a program that controls a 3 Axis drilling machine.

The GUI interfaces with an Arduino board.

I want the serial port connection to remain open throughout entire use of the GUI. I do not want to reopen the connection at the start of each different function. Is there a way to make the object a global or persistent variable? Would I need to define the object in the OpeningFcn?

My code below displays the Callback for pressing the Machine Run pushbutton. I only included up to the else because the code is irrelevant beyond that.

    function runMachine_Callback(hObject, eventdata, handles)
      % hObject    handle to runMachine (see GCBO)
      % eventdata  reserved - to be defined in a future version of MATLAB
      % handles    structure with handles and user data (see GUIDATA)
            status = {'Initializing MakerBot'}
            obj1 = instrfind('Type', 'serial', 'Port', 'COM3', 'Tag', '');
          % Create the serial port object if it does not exist
          % otherwise use the object that was found.
          if isempty(obj1)
              obj1 = serial('COM3');
          else
              fclose(obj1);
              obj1 = obj1(1)
          end
          fopen(obj1)
          set(handles.text5, 'String', status)
          status = 'Connected to MakerBot';
          sendXYZCoord = get(handles.checkbox2,'Value');
          if sendXYZCoord == 1
              mbStatus = 'Sending Coords';
              set(handles.text5, 'String', mbStatus);
              xCoord = get(handles.xCoord_text, 'String');
              yCoord = get(handles.yCoord_text, 'String');
              zCoord = get(handles.zCoord_text, 'String');
              xCoord_val = str2num(xCoord);
              yCoord_val = str2num(yCoord);
              zCoord_val = str2num(zCoord);
              fprintf(obj1, sprintf('[%s %s %s]',xCoord,yCoord,zCoord));
          else